Then you should be perfectly fine with it.
Bought, DL'd, and played through the campaign, plus the "I hate Mountains" Custom campaign. Don't lag on the regular campaign, but when it get's really intense on the custom campaign then I have an occasional lag spike. Although, it's the type of lag that's hardly at all noticeable and it's playable. I'm impressed, I'm gonna buy Oblivion GOTY delux in the coming weeks, see how I can handle that.