Mhz are not equal to processing power. The ARM cores of today are far more powerful than the ones released 15 years ago. What you ought to check are MIPS values, not clock speed.
The 3DS is fully capable of PS1 emulation, the graphics side of things will be greatly supported by the GPU.
Power-wise the 3DS stands between the Wii and the Gamecube, being closer to the Wii. It will most likely be able to emulate the exact same machines those two emulate, the rest is a matter of implementation and optimizing.
This post has been edited by Foxi4, Thu, April 12th, 2012 at 01:15