Dual Paladin for Uber Tristram?

Speaking from personal experience, the only thing you really speed up as a team is getting to

Lilith as she actually hides decently well and tends to have tons of mobs blocking the path. So unless your Smiter has an Eni, you do need to kill a fair few of them. For that specific purpose, a Sorc seemed to be the best partner. Not only because she can scout for

Lilith faster than any other class (to avoid going the wrong way) but because they're actually pretty good at taking down those specific mobs quickly, too.

All of the bosses on the other hand take noticeably longer to kill, simply because crushing becomes less and less effective with more people.

Combining Fana and

Salvation would be a nice gimmick but honestly, that is only in effect/relevant while you are killing Meph (which doesn't take long). Sometimes not even then because you can build your Smiter to not need it anyways. Soon as he drops (or before you get to him), there's no need for any sort of

Salvation. And if your Merc already offers Might and potentially

Concentration on top of that, you don't gain much otherwise. Certainly not enough to outweigh the negative scaling on CB.

All of that having been said, double-teaming is not a bad idea starting out, if you're not yet confident soloing it. If you want/need a hand/partner for that, you can reach out to me as well. Happy to help out (for free).