For now 5.00 will do as long as you patch games that require higher firmware. Not all game will respond well to the patching though. I haven't tried any of the GEN firmwares above 5.00. They might be good, but since I don't know where my psp 1000 is and my slim isn't easy to pandora because of a mod, I'm not going to try it out for now.
Founding father of the Wiibrew Packgen.
About 2 noob posts away from going ape sh*t