Sometimes it can be something as simple as your video drivers that's causing problems.
I have a Radeon 9600XT 128mb card. Decent, not the best but works fine with EQ and I'm not worried about any furture expansions... future games, yes, nothing with EQ though.
Funny thing is I downgraded my drivers several months ago and EQ runs better now. I used to get such bad lag that I had to play with all mods off except my own and I had the texture quality set to low.
Then I was playing in VG beta and I kept crashing every 5-20 mins of playing. Crashing so bad the computer would just reboot out of the blue. After some researching I found out other Radeon 9xxx users were running into the exact same problem and someone mentioned downgrading the drivers to a certain type would get rid of the problem. I did and sure enough the crashing stopped, but stranegly enough when I returned to EQ I noticed I was getting absolutely no lag what so ever. So I toyed around a bit and ended up putting on all mods and set my textures to high and I was still getting less lag than before with lower settings.
So I've been kinda scared to upgrade my drivers since then, lol.