Games are roughly 4 to 5 gigs. Some more, some less. Ninja Gaiden is like 10gigs, Fuzion Frenzy is 1 gig.
The two largest games I've seen yet are Ninja Gaiden and Kotor II. And I believe NG was close to 6gb. If it were 10, I would be reconsidering whether it should stay on my HDD or not.
Things like Halo 2 cannot be put on the stok hard drive because it is 5-6 GB. But halo 1 works fine
I don't know which
Halo 2 you backed up?...But my first setup was using a stock HDD and burned a copy of Halo 2 on it so I could mod some maps. The whole game fit plus some more room for a few emu's and roms. Halo 2 should be atleast a little TINY bit over 4gb, maybe right at the 4gb line. I'll have to go back to DVD2XBOX and put the game in to get an accurate reading.