The answer depends on the average buy-in of these SnGs. If this is at $5 SnGs or lower, it might be more profitable to move up, but if you're doing this well at like $20 or higher, I'd recommend sticking with the level you're at, at least for a while. And when you say average profit of 38%, I assume you mean that's your Return On Investment (ROI)% right?
A 38% ROI is very good at any level and pretty close to the maximum you can expect. I think as high as 45-50% is potentially sustainable, although a lot of people don't; I think it can be if you're at the right site, consistently playing with the "right type" of players. The play at Party Poker
was so perfect for me, I could sustain a 50% ROI in $20 SnGs over several months, but I seem to have no hope of anything nearly that lofty at Full Tilt.