It can depend a lot on how bad your local lots are. In SoCal softer rates are better to some extent. In general you only want as much spring as you need, compliance is a good thing. I'm running the Whiteline MaxG coilovers this season, starting the test with 5kg/5kg and likely going to move up to 6kg/7kg to get the balance I want.

The lots I run are moderate. Personally I expect that more compliance than one gets with 400/400 would be faster but I guess i'm just wondering how the majority ended up favoring the 400/400.

Because it was what was offered off the shelf and it seems to work well when coupled with limited camber (for tire wear on street cars) and stock-ish sways (for people who don't want to commit to a pair of swaybars on top of their $2k+ suspension).

Start jacking in the camber, be willing to do anything with swaybars and you end up in a different place than 400/400.

http://www.ft86club.com/forums/showthread.php?t=9936
http://www.ft86club.com/forums/showthread.php?t=120099

oinojo in that second thread won STX Nats last year fwiw, and others have put their cars top 10 with 400/400 and similar. It's certainly not 'put those springs on and win' because I've got similar rates (325/500) and I can't get my car set up for the life of me (much less drive it well) but that's part of the fun of Street Touring.
:burnrubber:

Interesting stuff. Thanks for that second link. I had not come across that one before. It sounds like it comes down to experimentation and personal preference to a large extent.

I think spring changes just come with experience and what you want the car to do where and when.

I ran 400/400 last year, but after reviewing what the car was doing to me...I decided to make a spring change for this year to combat that without effecting other car setup (IE - Same height/bars/camber...etc)

recommended tire psi for 235/40 federal 595ss with tein street flex and 17x9 +38 offset? first time ever autocross today and I didn't know what psi to run. so just did 38 psi all around cold. oversteered quite a bit... should I lower it?

38 is definitely high for most tires. I'm not familiar with your tire but I'd advise to start around 32 and go from there. Maybe someone that has run them before can be more specific.

Any recommendations for stock tire PSI setup?

Don't be too worried about it, you'll gain way more time thinking about your driving than whatever the tires are. For simplicity I'd say 34-35 psi cold, before your runs, after you start feeling confident drop 2-3 psi out of the front or rear if you feel like you lack grip on one end of the car, don't overcomplicate it, but if the change was too much drop the other end a bit to compensate. I think the tires might be a little grippier at lower pressures, maybe about 32 psi hot, but you may have to pump them back up before driving home or just ignore the tpms light and be fine rolling around on 27ish psi.

What would good starting tire pressures be for a D-Street BRZ on 225 Rivals?
Stock suspension.

Thanks.

I start at 26-28 square on 245 rivals on an STX car. I'm not sure how that translates, but don't be afraid to go low. Just be really attentive to how the tire is being worked, and drop pressures over a few runs while chalking the sidewall.

You can run low pressures on an STX car because of camber, though. Wouldn't go that way on camber-challenged stock car.

start at 30-32 psi at both ends and then adjust from there.

I am 400/350