If I were in your situation, I would be running 10 Arenas a week to bag your points on the 70s and when youre not doing that, get levelling a tank either by questing or boosting. Just what Id do.

It will open up more things for you to do both now and in the expansion. I would feel at a loose end in PvP right now if I just hit 70, multiboxing or not - while on one hand, you want the gear to stop etting slaughtered, on the other hand the expansions coming and you cant help knowing youre grinding towards a gear reset.

Under the circumstances I can only think that having a tank available will enhance your multiboxing options now and for a long time to come. Bank a tank is my advice!

But of course, your time your choice

Edit to add - I do realise that youve come back from a long break after hitting a bit of a funk with the levelling process. So having just hit 70, realising you might need something more and having someone say "Hey dude just roll a tank".......well, I can see why it might sound like glib advice. But if you can stomach the level again, it might be a way forward.

Edit 2 - having just read your last post PROPERLY, I realise my post is completely redundant. YAY!!! 8o