I have a PSX emulator on my Samsung Galaxy Note 8.0, but the lack of a proper controller meant we're stuck with using the touchscreen....spent 5 mins on Crash Bandicoot & pretty much gave up on it. So I think the PSP still beats pretty much any portable android device out there when it comes to PSX emulation.
^ I have a ps2 style USB controller on my Android PC and the PSX emulator with it is really good. If you were to get a decent controller I'm sure the experience would improve dramatically.
I play MGS on ePSXe for android sometimes on my phone. The controls, performance and graphics are all really good.
PSX emulation needs more than 1Ghz , I had a HTC Desire 1 with a 1ghz Snapdragon, while some games played okay, most were less than 20fps :/ None the less everything seems to work okay on a duel core UG-802 and it makes a pretty good emulation station for less than $40 ,aslong as n64 isnt what you need.