Hello. Long time browser first time poster here. So I have looked all over and can't really find much info pertaining to my question. Haven't gotten much from the vendors either. I am building a gen III 6.0 iron block engine that's going in a 5000lb daily driver. It will see the track but not much. More towing than track time. 2500-2800 yank stall, 4l60e with shift kit, vette servo, etc, 323 gears with posi unit, Fresh 799 heads, stock rebuilt bottom end, shorties, 30lb injectors, new stock lifters, reuse stock pushrods, and an aftermarket cam. Therein lies my question. I am looking at a 212/218 with .550ish cam. This should give me gobs of low end power and still have some top end. I've got the comp version on a 115 and a set of psi cylindrical springs with tool steel retainers which I'm not sure if I should use. The btr can run on 295 lbs of seat pressure(blue ls6 springs), while the comp needs 375 lbs. Is this because of the xfi lobes? Would I be better off keeping the heavy cylindrical springs & comp cam? I'm worried that if the springs are that stiff in comparison to the blue ls6 springs that I'll run into problems with longevity. I could be dead wrong to. Any info would be greatly appreciated