If you get a large hard drive, (the larger, the better), and only use the first 80gb of it, your performance should improve measureably. That is called "short stroking"
Performance improves for two reasons:
1) Data transfer rates. Larger hard drives are denser, so more data can pass under the read/write heads per revolution. Also, the first(outer) cylinders of the drive contain more sectors than the inner ones. More sectors passing under the heads per revolution results in faster data transfer rates.
2) Reduced seek times. Since your 80gb of data will be confined to a limited number of cylinders, the access arm will have a more limited range of positions. Since short seeks are faster than long ones, your system will average less than average seek times.
I would suggest something in the 1tb range. Use the remaining space for backups, or even not at all.
Do, though consider the 80gb intel X25-M gen 2 version for the best performance.