All answers can be found in the Bhagavad-gita.

"All of them - as they surrender unto Me, I reward accordingly." (BG 4:11).
So, obviously, the greater your surrender, the greater your reward.

In the Bhagavad-gita, chapter 12, verses 8 through 11, Krishna says, in a nutshell, "if you can't do this, then at least do this other thing... and if you can't do that, at least try to do..."

So, IMHO, you can't be any more inclusive than the words of Krishna. I don't know ISKCON's position. Maybe they are more hard-line than Krishna.