Necro-ing this to update with my progress on learning.
I've been on DIY Billies for almost a year now. I went with the following parts: NB B8, 550/350 springs, 5" allstar sleeves, delrin lower washers, poly upper spring seats, integra speedthane cut down to 40mm iirc, Maruha top hats (all 4), new OEM top hat bushings (all 4). I loved this setup, but when I put on some stickier tires, it started to show that softer springs weren't great for the front where it was rubbing more often than I would like.
Ordered 700/400 and what a world of difference it makes. The 550/350 setup felt, bouncier? the 700/400 setup feels firm and planted. I love it. Paired with Mazda Comp motor mounts, a M1 hardcore double diag, NB2 seats (driver foamectomy), a properly depowered rack (MiataSource), and it feels so good. Much racecar. Trackday bro. Another weakness has shown. I really need sway bars. Stock sways with this setup is not cutting it. Next on the list. Just need to do more research.

I'm sitting right around 4.75" pinch weld height, 15x7 205/50 Maxxis VR-1, no fender roll, Supermiata Dual Duty alignment, aaand there's nothing open cause corona.
pictures of everything here: imgur link

Those shocks are not happy with those springs.

you would think, right? given that when I had 550/350 on, going through bumpy parking lot was bouncy. you could feel the underdamped-ness. but since throwing on the higher rate springs, I don't notice it. I did ask a well versed in the diy billie guy about going to 700/400 on the shocks I have and he said he's used 800/500 without revalving. and he actually sees track time. I don't expect them to last forever.

What was the total cost for that setup?

If I use the price of the summit racing brand springs (550/350) the price was about $1040 after 6% state tax. Unfortunately at the time of ordering, they didn't have the Summit brand 550 spring, so I had to pay a little extra and get the QA1 (literally the same thing but still has the logo on vs summit which is acetone wiped logo removed), the actual cost of the 550/350 setup was about $1060. I tried the spring rates but when I put stickier tires on, it had a lot of body roll. I was rubbing a lot more (I swear they're wider than they say they are) so I opted to go stiffer all around. In this case I went with hyperco because they don't make the summit springs in 7" long that high of a spring rate, so the cost then (ignoring the first pair) is now about $1130. Price and availability will definitely change and your local tax is likely different. Also,I don't have helper springs, so when on the lift (2 post lift) when full droop the springs don't touch the top hats, but I've been told it's fine when you're driving.

It's not about lasting forever. It's about working well or not. I don't have this standpoint from a lack of experience.

If you're enjoying your pogo stick, then carry on. I'm simply telling you the shocks are not up to those springs. If you can't tell the difference, then good for your wallet. :rofl:

Food for thought: you can literally drive anything on track. "Not breaking" isn't the same thing as "this is something i'd choose to do over other things."

this right here is why. ignorance is bliss or something right? once you feel better, you start to see why things are important. and then it starts to make sense why buying new bilsteins and having them revalved and then all new hardware starts to add up to xida prices. it's not a pogo stick. it feels smoother than the 550/350 to me. and i didn't lose my bank account trying to find out what I like. for now, it's a fun street car, i will autox it when they allow events, and since it has a roll bar it can go on track but i'm not going to push that until i have sways.

Yup. This is an important concept. If you drive slowly enough and don't know what a good handling car feels like, a bone stock Prius is the perfect track car. Nothing more reliable, safer, better resale or lower consumables.

Am I the only one who finds it peculiar that significantly higher spring rates have somehow caused a need for stiffer sway bars?

Then again, I recently replaced my FM rear sway with stock and softened my front one and now enjoy life more.

In the context of how this thread went and OP's grasp on the wonderful world of suspension, no i don't find it peculiar at all.

Those two things are not directly related. The reason a tuner would add bigger sway bars is to improve transitional response and retain any camber gain. This is directly related to roll moment. More Tire grip increases roll moment. The other factor, as it pertains to modifying OEM production suspensions, is that when you lower a car past its intended intended and optimize roll centers, you lose effective roll stiffness. This requires bigger sway bars to merely retain OEM roll stiffness.

One of the reasons that we always recommend sticking with smaller or stock sway bars, at taller ride heights if ride quality is a primary concern.

I put the grippier tires on before doing the spring swap, and excessive roll is something I noticed right away. I was rubbing much more often, even when going straight and braking hard. Which is why I thought naturally to put on stiffer springs. When discussing with another experienced DIY Bilstein builder, he recommended going up in spring weight with added grip, because of the same reason you said. But now you have me wondering if I could have kept the 550/350 and put on bigger a sway bar, since I am still running stock sways.

At some point I'll just ball out and buy Xidas and do it right. The way things are going, the car will be a fun weekend backroad car and whenever autox comes back, I'll do that. I'm not aiming for the ultimate competitive car. I'm not doing spec miata. I'm not doing professional level racing. You learn from mistakes. I've seen locals track on much worse, hell one of my buddies didn't even know what suspension he had on the car.

Sway bars are a torsion spring. They borrow spring rate from one side of the car to assist the other side.