Sorry, I don't believe that 3DS will be able to run a PSX emulator.
I'm bored in class so explaining my reasoning will kill sometime. Don't read this if it'll waste your time.
The reason why emulators such as SNES, GBA, N64 or DS is possible in certain platforms. It's because the computing power of what ever we are emulating with is exponentially powerful than that of their predecessor.
Think about it in a theoretical concept. Let us say that a PSX has a computing power of 3 and our current technology allows us to have a computing power of 15. Since the system emulating need to have a exponentially powerful computing power, we will say that the theoretical minimum requirement in order to emulate a PSX is 3^2 = 9. We are therefore able to emulate a PSX with our current system.
Now let us assume what you said is true, that a 3DS is more powerful than a PSX. Of course 3DS does not have as much computational power as our best systems right now, so lets give it a good 8 rating, well above the PSX. However, remember that the required computing power of PSX is 3^2 = 9, thus 3DS fails to fall withing the requirements.
If computing power increases linearly, as statistics have shown, our technology cannot catch up with the increase in the requirement of computing power in order to emulate such systems. Our computational power will increase from 15 then 17,19,21 and so on...While the systems developed from our current technology will increase like that of a 3DS from 8,10,12,14 and so on. Our requirement will be increasing from 8^2,10^2,12^2,14^2....
and blah blah blah, got lazy XD