22 ( +1 | -1 ) I played 4 b3 once at yahoo a long time ago. Black announced that in 9 years of playing the benko, he had never seen that move. He then promptly destroyed my position and I never tried it again.
31 ( +1 | -1 ) 4... a6 is practically a wasted move. By playing 4. b3, White is announcing that he's not going to take the pawn anyway, and 4... a6 doesn't improve black's position in any way. Either 4... bxc4, opening the b-file, or 4... g6 is a good response. If you're really concerned about cxb5 (even though white has already played b3) you can play 4... Bb7.
25 ( +1 | -1 ) well said atrifix. I might also add that playing the Benko Gambit "without sacrificing a pawn!" undermines the aim of the defense: the opening of the a and b files. If memory serves me correctly, Black played 4...bxc4 with excellent counterplay.
42 ( +1 | -1 ) 4... bxc44....bxc4 might be good although I have some apprehensions on playing it. It only opens the b file and allows white to maintain a pawn on c4. White can even fight for the b file since the a file is not open as in the normal benko gambit lines. I haven't tried it though. Anyone who has a sample game featuring this line, pls post it here. Any other suggestions would be greatly appreciated.