I have the stock rear springs on my 2002 zr500LE which are .452 90deg I believe.
I weigh around 185lbs.
I just added taller 3.25in spring retainers to add more preload hoping this will help since i have it studded.

How can I tell if im going to bottom out? How far should it sag from original height once I climb on (inches)...that should be stiff enough for not bottoming out once riding?
Alot of trail riding powder riding sometimes. No real jumping and such. Only some rough trails ya know.

thats not always the case...i have a 162" on my ZR800 with a king cat rear suspension and that dont move at all when i sit on the seat, barely when i jump on it even, but i did bottom that out last year since i thought i should jump roads with it (bad idea). Just keep an eye on your tunnel and watch for scrape marks, i would think youd hear the studs hit the tunnel. just be easy on it.

Yeah im not into jumping and being rough with it so I think Ill be fine.
I only weigh 185 and the roughest it will see if some rough trails etc.