The general rule of thumb to emulate a console you must have at least 9x the power in order to do so. The PS3 doesn't come very close to that for the GCN at all.
Let me let you in on a little secret.... That 9x (or more commonly I see it as 10x) is a load of bullocks and doesn't hold true in a single case anywhere.
SNES 3.78mhz, in a completely ASM highly optimized emu (see Zsnes) it requires 400-600mhz x86 with a compatibility of about 80% (this excludes all special chip games and many other "broken" games that rely very heavily on special timings) and most games at that point will run without frameskipping. That's already a machine 100x faster, and to get 100% accurate emulation (see bSNES), you need a CPU capable of reaching 3+ghz, nearly 1000x faster.
N64 98mhz RISC processor, to get any games running playable you need at least a 500mhz x86 cpu and a 200mhz Glide based graphics card (see UltraHLE) Depending on how you want to judge the graphics card involved, you could say between 5 to 7 times. To get the most accurate emulator to accurately emulate all effects (especially the devious "frame buffer" effects) you need a CPU capable of single threaded performance above 3ghz (or 30x+)
PS2 300mhz~, to get the feeblest of 2D games working you need a modern dual core+ processor at 2+ghz. 3D games can require anything from 3-5ghz+ to maintain full speed as well as a fairly advanced video card with high bandwidth (GDDR5+ 128bit+ interface if you want anything about native res), so again depending on how you judge graphic card in this, you're looking at between 6-15x+ to get an emulator that runs about 70% of games working full speed.
Wii 733mhz~, I can get skyward sword running full speed fairly easily on my 3.5ghz quad core unlocked AMD and the only thing you really need is a decent video card to back it up. Most games don't require nearly as hefty a machine, my 2.5ghz laptop for example can run Twilight Princess full speed with a few bloom hacks and minor slowdown on Hylia Field. That puts it between 3-5x as powerful.
The emulation "rule of thumb" is complete and total bullocks... The complexity of a system and how closely it resembles modern PC hardware is the real determining factor... That's why the much more 'powerful" Wii is so much easier to emulate than the less 'powerful' PS2. The PS2's design is both much more complex, and much less like a PC. The PS2 doesn't have a graphics "chip" per se, but rather it has 2 Vector Units, where as the Wii has a more or less standard ATi graphics chip with a few tweaks and features just for the system. The rest can be almost mapped 1:1 to already existing functions in existing modern graphics cards.