Why not ask Brandon at SV? He knows his guns better than anyone else and knows what his sponsored shooters use. With that said, I like 4 holes for 38 super with the SV comp.
If 38 SC brass is not an issue, go with SuperComp. More load choices and easier to make completely reliable. No searching for SV magazines or playing with magazine spacers. My 2 cents worth.
If you have the up front money and the patience to wait a year for delivery, get the SV, its worth it. If not get the STI and start using it right away.
I have a little pressure on it naturally but don't really push down. I use it more to resist recoil. The brand of thumbrest may make a difference in how you use it