^QFT
There are so many bad spring rate coilover sets on the market.

450/350 isn't really that bad, although with the RB bar it will understeer without a rear bar to balance it out. Not saying it's ideal, but it can get the job done.

I disagree. I field calls all the time from people who have trouble with oversteer after buying coilovers with mismatched spring rates. 450/350 will never handle correctly, regardless of what sways you throw at it.

450/350 will oversteer in all situations regardless of swaybar combo, BTW.

Then I must have something really far off on my setup. I have 450/350 on koni yellow with Millen Motorsports front bar (solid 1") and stock rear, and I have issues with understeer.

(That said, I have a set of Xida sitting in a box waiting to go on.)

I wasn't going to bother following up as it's a comprised setup regardless, but with RB front / 11mm rear at 450/350 koni sports I too suffered from understeer, as stated. Saying it will oversteer in all situations is untrue. There must be another variable at play. Lack of rear travel, driving styles, etc.

Consider that Spec Miatas run 700/375 with a slightly larger rear bar, but you claim to have understeer with 450/350. By that math, SMs should push horribly, but they don't. If you two have issues with understeer, it's setup or old/bad tires.

Sounds like you guys have stock or FM alignments.

1.5 year old RE-71r, 5"f, 5.25" rear, 2/1.5camber, -0.3* toe in front, 0 rear (just how it ended up, need to fix that).

Weights are 2494 with driver

FL660 FR600
LR638 RR595.

And again, 450/350 on koni yellow with 1" solid front and stock 1990 rear.

If you can tell me why it understeers that would be great, because everything I have read says it shouldn't but it does. Could also be inexperianced driver?

Camber is maxed for the ride height. I am adding ELBJs to fix that while I put the Xidas on this winter.

Driving style. Are you pushing into the apex to scrub speed?

So you have front toe in and you wonder why the car pushes?

e: 0.3deg toe in on a 23" tire is 1/8" total front toe in. If you look up "how to make my car not rotate at all under any circumstances", you'll find "front toe in". Fix your awful alignment :)

This is the reason I posted up the specs. It is -0.3* total toe. Is that enough to over ride the mismatched spring rates? I am still learning about all this stuff and make no claims to have done anything right.

Shoot, ya ninja edited me. That answers my question though.

Yes, 1/8" front toe in is more than enough to compensate for improper spring rates. That is causing all of your problems.

Just to back up the recommendations for the smaller RB 1.125" sway bar:
Most MSM buyers prefer the RB 1.125" front sway bar despite the 1.25" being recommended by RB (I originally had the larger bar and switched to the 1.125" bar after I'd had a track day with it).
The OEM MSM rear sway bar is 14mm and is typically kept.