An sp150 should get you just over 500, depending on your setup. Sp130 or sp140 (if those are still sold) would work for that fps, with perfect compression and the right setup.
It's really a trial and error thing, and depends on the rifle. I'm not especially familiar with the PDI spring rating system, but those are laylax's.
Also, running ~600 fps (this could be off by +/- 50 fps, I really don't know how that converts to .2's at that speed, without doing the F=ma crap) isn't smart in any setup. However, I'm a bit surprised the zero trigger is the first thing showing wear, given its design (it puts very minimal stress on the sears).
It's really a trial and error thing, and depends on the rifle. I'm not especially familiar with the PDI spring rating system, but those are laylax's.
Also, running ~600 fps (this could be off by +/- 50 fps, I really don't know how that converts to .2's at that speed, without doing the F=ma crap) isn't smart in any setup. However, I'm a bit surprised the zero trigger is the first thing showing wear, given its design (it puts very minimal stress on the sears).