sanjoy.bose
Journeyman
are u building a server?
Asus X54 will be the best option I think.But if you need much better performance then you have to get i5, which will cost you atleast around 32k(a good laptop can be bought at that price)
If you're sure you just want to make your laptop as download rig, then brazos (E-450) is fine. But if you intend to use it for other apps, then in the long run, it will surely feel underpowered. So, at least go for Pentium Dual Core or i3 (coupled with 4GB of RAM). And as Sam said, don't club SSD with brazos as they're too slow to take advantage of SSD. For SSD, look out for Crucial m4.
Why dont you think about the Atom based netbooks? Works great and long.