Feingold and Wellstone would have ensured Gore win in Wisconsin, Iowa, and Minnesota. But it ended up that Gore won those anyway.
If he went with one of those two he would have lost Florida by 2-3%.
You're probably right about Florida. But I think Gore could have won Ohio by picking one of those two combined with NOT giving up on the state by pulling his ads.
This is all in hindsight of course. I wasn't critical of the Lieberman pick when it was first made. Its weakness was only apparent after (1) the VP debate and (2) Gore unveiled his (very successful) "people vs. the powerful" message at the convention, which Lieberman didn't mesh well with.