What about just taking 3 or 4 FULL buyins and expieriment. Just go out and play ur regular game. No short buy in, no double up. Just play. Even write the buyins off. That way u can play ur regular game and if u lose, u lose. Cause I get the feeling u are a very good player (from ur posts). I would hate to see u doing less than optimal cause of ur fear for larger amounts.
I was very scared when i moved to $50NL (i know it not the same as $400NL). But i had 4 buy ins put aside. It was my buffer, if i lost them oh well. But i was determined. If the players at this higher level are gooing to beat me. They are going to have to beat my A game. Not my shortstacked and scared game.
Well i hope this helps. I know i am not at ur game level. But i think it applies still in theory. Go out there man with 3 buyins or so and make them beat ur A game!