Location, location, location. That was the issue, not being able to keep the cache on a separate partition. With dial-up I don't want to kill the browser cache or cookies on exit, that just slows browsing for me.
The browser size wasn't an issue (I saw the resize cache and memory usage options), I have lots of space on both partitions on my primary HDD and huge amounts on my secondary HDD. I just didn't want in on my C drive.
I'm well aware that it is still beta but can you move the location of the cache in 8.51 if not I doubt that that will be an option in the final 9.0 as i isn't mentioned in the whats new (but that is a very small detail).
Unfortunately, it was a combination of things not just this that made me uninstall it.