Which spring rate for road?
 

What do you suggest as spring rate for sprty use on windy roads?
I saw everything, from 3k to 8k...

windy roads, canyon runs and so on .. are much closer to street .. those still are public roads, public roads, that usually get speed limits fit for even less sporty cars. And public roads where are way more uncontrolled variables and thus where safety margin should be wider. Hence i always considered such driving way closer to normal daily driving then to track .. and probably would choose spring rates similar to DD. There won't be driving on 8-10/10 limit as on track, most probably, if DD is 3/10, then eg. 4-5/10. No big side-Gs, no speed at traction/grip limit at every turn. Hence why compromise comfort if you don't gain for that what pros stiffer springrates may bring, just cons.

~3-4 front, ~4-5 rear would be good...

I ran 3.8F/4.5R Swift BRZ Sport springs and I think they're a very good spring rate for spirited/sporty street duty.

Addendum:
I should add that these springs combined with front camber plates (Raceseng) lowered the car more than advertised, by 1.5" front and 1.25" rear. This had the car *hard* on the front bump stops and resulted in an intolerable ride on the street. I cut down the front bump stops and had spring spacers machined to raise the front by 0.25". This improved the ride a lot, but still intolerable over the smallest bumps on the street.

I *think* that without the camber plates (which reduce bump travel by ~15-20mm) these springs would be fine with stock struts.
But RCE Yellows at 4.5F/4.5R and 0.8" lower than stock are probably a safer bet...

4K 5K or 5k square

I'm satisfied with 4.5k front and rear with 20mm drop.
RCE yellows. Feels extremely balanced for street/canyon.

^^^ For stock struts/shocks, IMO RCE Yellows are the way to go. -0.8" (20mm) lower than stock and about 50% stiffer spring rates. Fun with no worries :)

Lower than that, you'll want to get Bilsteins for additional front bump travel and better damping than stock.

I find 5K too soft and will likely be going to 6K with my next coils, albeit with vastly better damping so there is no trade off in terms of comfort

Also keep in mind that the soft/hard adjustment has so much variability that you can make even 5K coilovers unlivable on anything but a smooth road and at the opposite end of the adjustment range make them so wafty that you feel like you're in a Rolls

Damping > spring rate.

uh oh, I can feel it on its way... oh no, it's

[serious mode]
You have noticed there is a wide variation in suggested spring rates. That's because there is no "best" answer. Different people have need wants and importantly, different impressions of how a particular rate feels. 6k with good damping might be acceptable to you but might too firm for someone else. The general condition of the roads you drive on will also have a bearing on this. The best solution would be to get rides in cars with differing set ups. If you can't do that, have a chat to either Andrew at RaceCompEngineering or Mike at CounterSpaceGarage. Explain what you are after, what you wanting to achieve and take their advice. I would suggest purchasing from who ever is closest to your home.
Axiom: quality costs.
[/serious mode]

depends on road conditions etc near you but 6k has been good to me. on bad roads its a bit too firm.

Sorry to re-up, I almost made up my mind...
As lack of coilovers with reasonable price in Europe, I reduced my choices between 3 types of HKS (F6/R4, F5/R5, F4/R4) and ST XTA (F6/R5).
Suggestions?

I've ridden in a car with the STs, feels OEM+, they're amazing. I have no experience with the HKS, but they seem popular.

I have Ohlins which had the 4k F and 3K rear. I replaced the rear with a 4K spring and am now going to 5K F and 5K rear. I may go 6K alll around in the future.

I've also had the stock dampers with RCE yellows which felt good.

Good news is springs are relatively cheap to change out. I'm learning a lot by changing things up.

I would say St with flipped springs or 5k springs up front.