I shoot a 50# bow with the Eclipse 145 w/25 gr. srew-in adapt. I have great flight, but would I benefit from the 135 gr. w/42 gr. adapt. ( 1 3/16th ) cut or the 155 w/25 gr. adapt. ( 1 5/16 th ) cut. Or just stay where I am. South Carolina has THICK woods, I need quick kills and great blood trails. This would be on the assumption of a well placed arrow. 50 yards here is like 100 in a clear cut.
Just a heads up, you'll need the 25 grain short adapter for either one of those, the 42 is too long for the 4 Blade Eclipse. I might still have some 41 grain mediums around that will probably work though.
Shot placement and sharpness trumps everything else, but they are all good heads. That's part of the fun, is experimenting and trying new things, but they will all work fine if you do your part.
As Dr. Ashby has recently demonstrated in his broadhead penetration and lethality tests, shafts weighted front of center (FoC) have better penetration. So as long as they shoot well, the heaver the head you can get away with, the better the penetration. Four-blades give better blood trails. Two-blades give better penetration, esp. with bone hits. Eclipse are great heads. Once you get 'em sharp, they stay that way.