We have an SQL 2005 database backend for our website, currently about 10GB in size. There are a lot more reads than writes, though I don\'t have the exact statistics.
We
I would also recommend establishing a set of baseline values which allows you to both do some more founded predictions than just putting your finger in the air (or asking StackOverflow, seems vaguely and oddly similar those two concepts).
With some baseline values you can also measure the effectiveness of your changes and be a good foundation for future upgrades...
(If not known, pick up some literature (or wikipedia) on Performance Engineering. It's a whole branch of stuff that deals with just this type of problems).