My rig has been postponed due to finances, but if you look in my sig that's about as far as you can push the GPU on the stock 450W PSU for the SG05-450 - Sapphire Radeon 6950 2GB revision 2 (doesn't need cutting the case either).
Miahallen's MAX11L which inspired my rig did have a GTX480 (with some case mods), but after extensive testing it seemed a little too much for the 450W PSU.
There's a few worklogs for ATX PSU mods around - go Google - but to be honest I don't see much point when you have the SG07 available. By the time you've bought the SG05, cut it up, bought and dropped in a decent PSU just so you can fit a graphics card that will almost certainly be too big anyway you could've just got the SG07 with its 600W PSU and fit anything in it.
Of course I fully support modding for the sheer hell of it!