I'm currently in the process of converting a setting that combines Bubblegum Crisis with Akira from the Hero system. There are two types of psioncs in the setting: Psychokinesis (dealing with the physical world), and Espers (dealing with mind-to-mind powers). I had originally intended to use the d20Modern system to do this, but found that the base/advanced class system interfered with the flavor of the setting. How can you have 8 year olds flinging around tanks with their minds if the youngest character has to be at least 15?
That's when I decided to take the plunge with SC, and boy am I glad I did. Not only can you start out with psionic powers and not be diminished by having to essentially wade through three levels of fluff levels (minimum), but you already use the VP/WP system for added deadliness and realism, AND the NPCs are easier to manage. Then the much better autofire system is leaps and bounds above the d20M way. It's like upgrading from a Gremlin to a Corvette.
Anyways, back to the point. I'm going to try the two classes with powers taken like a sorcerer, powered by power points. The big difference was inspired by the new 4ed DnD stuff I heard about. Instead of working with a certain amount of points per day, they are given a much smaller pool (about 1/4 IIRC), and recover at a certain rate. This allows them to be more useful at lower levels over a longer period of time, rather than blowing their wad and being useless the rest of the day. Of course, I had to make entirely new powers for the psychokinetic (or PK as they're known), in order to better represent them, but they practically wrote themselves, once I figured out the way psionics work in 3.5.