Granted I know nothing, but as optifine is just a graphical enhancer, I can't see how it could have any effect at all. I mean installing a texture pack doesn't. So I think you should be fine, even if you kept it installed. I have however heard that it doesn't work w this mod pack (due to the version of part of it I assume). But again, I know nothing, if anyone says anything different from what I just said, believe them, not me.