I use this chart all the time:
http://www.ackits.com/index.cfm?fuseaction=Chart
Generically speaking, 350+psi on the high side is probably too high, even if condensor temps are high.
You could start by trying to remove some refridgerant, but you might have a different problem if the low side pressures are in check. I'm not well-enough versed in A/C to know what that would be, though....maybe something with the expansion valve? Or a blockage in the orifice tube?