Sweet! I was on the fence about either the BYOC or the GGG one, but GGG had theirs on sale(as they often do). As far as the opamps go, I ended up with the TI LF353P. Quieter, higher overall bandwidth and a flatter EQ when compared to the 4558. In my experience opamp swaps don't really do a whole lot when you're slamming the clipping section full on. I use mine as a boost and an amp tightener, so not a lot of clipping and it makes a difference. I would like to try the NE5532.
I'm running on 18volts and really like that improvement. Increased headroom and more lively dynamics. Doesn't "choke" my pinches like on 9v and my palm mutes have more initial attack. I'd check about whether or not your kit's components are able to do that or not.
For fun: some opamp schemes
First one's JRC4558, second's NE5532. Pretty dissimilar.

