RE: Benching and thumbs
Do you mean a thumbless grip as in having your thumbs round the same side as your fingers? I do that a lot, especially with close grip benchand things like tricep pushdowns, I think because from gymnastics thats the most familiar grip for me to use. But I consciously try to avoid slipping into doing it that way, because i found that when I used my thumbs around the bar , it felt like it hit my inner triceps harder. Not sure why, but anyway now I try to do it the normal way.