Actually the HP 50g speed is hampered by how the OS actually runs on a Saturn processor emulator layer, not directly as an ARM-written OS, so it's about 7 times faster than the 48g for the most part. The HP Prime, on the other hand, had an OS rewritten from scratch for the ARM processor and the processor is even faster, so there is a major difference (although the rewrite resulted in many glitches). ARM ASM on the 50g must be ridiculously fast too, though.
On the HP Prime you can graph almost everything instantly.