Because you don't want to make the walls thinner. Ever. Especially with boost. And the amoung of extra displacement you would have is not even worth discussing.
Also while 4032 is "more like" OEM pistons, its still not OEM pistons so you would still want to run slightly looser tolerances which would result in noise/wear. How much noise and how much wear all depends on how good you are at calculating/harmonizing all this crap and how good your machinist/engine builder is.

I mean there's a reason shops charge hefty sums for complete built engines.

 

I'm almost positive that all FM strokers are 84.5, they probably have special blocks though I disagree with your post on bore not being noticeable, just look at the spool data on a 1.6 vs 1.8 (94-97).

 

78.0 to 83.0 is drastically more than 83 to 84.5
And that's ignoring lots of other stuff like head design, stroke, manifold design, etc etc. If you went from 1.8 to 2.0 then your argument would make more sense.

But hey I'm always for moar displacement so punch it out as much as you can on your engine...make sure to post results of 85+ bore and boost

 

I don't have to, FM has hundreds of 84.5's on the road.

 

85mm is too big of an overbore for a forced induction motor. Supertech doesn't make an 84.5mm piston. You're trying awfully hard to convince the OP to buy parts that don't actually exist.

 

Your thread inspired me to look into supertechs, id like to say thank you for posting them as a good option. I love the sounds of a stronger piston without soo much expansion/contraction.