A stiffer spring will lower your SD over the chrono a little bit. The G20 does open pretty fast with heavier loads. It frankly doesn't matter. I put the stock spring back in because the recoil feels much less intense like that. I use Power Pistol and it works fine with 180 gr bullets at 1150 fps. Thats plenty stout for me.
Yes, I post using a phone so my spelling sucks.
Converting Hornady owners to Dillon
one owner at a time.