Definitely on the same tier but I think I'd go with Gortat. KG already brings pretty much everything Varejao does. Yes he'd provide more rebounding, but if we had 4 above average rebounders in KG, Gortat, Wilcox, and Sullinger that wouldn't be a problem.
Varejao excels at picking up hustle baskets but Gortat is a significantly better offensive player. Gortat does more things on the court than Varejao, whereas Varejao is elite at things that Gortat can do anyway (rebounding, help defense).
Although this is one of those cases where we wouldn't know unless we saw both, the way our team is constructed I'd lean toward the interior presence (especially since we don't have one) and the better rim protector/shot blocker.