I was worried about the 2Gb needed for the second disc, but I reckon getting rid of the masses of Forza 2 stuff I've got saved (replays, decals, DLC, setups) I can probably clear plenty.
I guess now would be the time to screenshot my Sonic the Hedgehog skin (that's been kicking around for about 8 months) before consigning it to the great scrapheap in the sky.
Now all that concerns me is that stupid forced revving it does before the lights.