Raspberry Pi CPU Power.
 
Rated at 700MHz, the ARM CPU in the Raspberry is supposed to be equal to a Pentium II @ 800MHz. The thing is this – under emulation tests of other systems on the R-Pi shows this to be a lot stronger than a Pentium II. On the 68KMLA forums, they have the R-Pis running 68K Macintosh systems emulation from the poultry 128K to the color Macs up to a Quadra System. Emulating a 68K CPU at full speed requires much more than a Pentium II CPU. At minimum it requires a Pentium III.
 
The emulations I have tested it for are the 6502 CPU Machines: Apple II, Atari, Commodore 64 and Vic 20. Other machines I have also tested were the Z80 systems, both of which can be done on a Pentium II at around 500MHz at full speed. But I found out that under MAME (Multiple Arcade Machine Emulator) the Raspberry Pi was running video games like Joust, Defender, StarGate and Robotron – all 68K CPU based arcade machines and at full speed. This is not possible with a Pentium II even at 800MHz with at least some slowing down during game play. I have several Pentium II systems running Linux, the Raspberry Pi surpasses them on many levels and my PIIs do have SSD - Solid State Drives.
 
Further more, sites I have seen stated that they has emulated the PowerPC Macintosh with System 7 and 8, and at least 1 French site claims to have emulated a PowerPC or G3 and ran OSX on it. Emulating a PowerPC alone takes a Pentium 4 at double the speed of the emulated CPU. A G3 CPU in order to have OSX would take double that kind of processing power.
 
There are other things to consider, most of which can be taken cared of by the GPU in terms of graphics for the emulated machine. So the question lies, at what level is the Raspberry Pi at when compared to an Intel system? In trying to answer this, I have to say that it is at about the level of an Intel Atom CPU of equal clock speed. The Intel Atom is a single core CPU that is used in many NetBook small form factor laptops, which is somewhere at a P4 CPU but deliberately crippled at P3 levels.

PiMame and RetroPi configuration code overclocks the R-Pi to 900MHz. I reset the clock to 700MHz with the R-Pi Config and though a couple of more involved games tend to slow down, most games seem to play well at 700MHz as they do on 900MHz.
 
So, if you are playing either RetroPi or PiMame and did not change its configuration, the OS sets overclocking to 900MHz.
 
The R-Pi can handle the overclocking of 1000MHz (1GHz), it's in the R-Pi config settings, but I would put in the heat sinks if you are going to over clock the poor R-Pi at anything over 700MHz.