It really depends on what you're doing, but I doubt you'll notice that much of a difference. If anything I'd go with the bigger cache I guess. Although if uses large files that'll fill up in like 1/10 of a second. If you really want to improve drive performance you've got to switch to the new SSD's which have readspeeds over 200Mb/s and write speeds of anywhere from 70-170 Mb/s.
What most people around here are doing is getting an 80MB Intel X-25M ($220) and then also getting a set of 1TB convential drives for data storage. You could always go for an SSD other than the Intel series and get something a bit smaller. The smallest I would go with a block for an operating system and programs is about 32GB. That won't give you much room for large programs but it will be enough space for a 64-bit installation of windows with all the normal programs, drivers
, etc. You'd store all of your other stuff on the conventional drives. If you have the cash, do something like this:
Kingston 64GB SSDNow V
2 x 1.5 TB Seagate Barracuda
Total Comes to $350
Now you can boot up to two operating systems off your SSD, preferably one. All your system actions will be executed extremely fast because they're running off an SSD. I.E. Explorer, Firefox, etc. Anytime you want to use a huge program or game, you can just install and run it off one of the higher end conventional drives which will still run well they're just not as fast. You could get away with one of the larger drives, or you could just use it as a backup disk.