I think we touched base on this with that cut blend I mentioned. I'll go into some more depth (at least for me)
While cutting, I have run test/tren at 750 ea a week. I never gain strength but it hardens and thins my skin like crazy. While bulking or strength training on that dose I'm usually never left disappointed when I max out.
I think 500/750 is a great combo. The sides aren't going to be as pronounced (750/750 usually requires the use of a bit of Viagra and I'm not to pleasant to be around).
I've heard alot about low test/high tren but it's never been my cup of tea. It's all based on how your body reacts to it. If your getting good results on 500/750 keep it at that!