I'd use both but use the smaller one for windows and installs only, then the 300Gb for storage, movies, downloads, music.
Boot up takes along time with bigger hardrives so it will speed things up a bit and organize things better.
Opteron 175 + Scythe Infinity
2 gigs corsair XMS DDR 400
XFX geforce 6800 XT
30G Maxtor + 250G Maxtor
"Let's face it, we're not changing the world. We're building a product that helps people buy more crap - and watch porn." -- Seagate CEO Bill Watkins