The Pandora and N900 hardware is very similar, don't mind the different chipset versions - the only difference is that the N900 version is meant for use with a GSM phone.

Both units run at 600MHz, and both units have 256MB of RAM. GPU, DSP, FPU, Neon, everything's the same. In other words, the HW performance is similar, there's no difference there.

The differences are in the extra hardware keys on the Pandora (that's pretty significant), and then it's down to differences in software (UI and the like). Which may of course be significant, one way or the other.