A little off topic here.
I used to single box raid, so i can be better at multiboxing, that was my goal for years. I've got into us top guild, so i could learn more, get a better grip on my abilities....so once more i can multibox better, this is main reason why I dps'ed on my shaman as my main, and my so called main alt was always my paladin tank.
It has been like that for almost 3 years, until recently....there is nothing left to box on live servers(for me)
I haven't boxed on live for a long time now, Ive been single box raiding on my warlock, shaman and paladin, but i realized my goal was not multiboxing anymore.
In the beggining of wotlk, we had many challenges ahead of us, multiboxing or not, they were there. Boxing brand new heroics was tons of fun, going there with a tank that had 18k hp and not even def capped, shamans with 14k hp and under 1k spl damage.....those are some fond memories for me.
Upgrading gear back then made huge difference in doing those instances, but now its a bit different, if Your toons have all heroic gear, You will be able to do last few 5 mans of wotlk(3.3), it might take a bit more learning and getting used to your teams, but you will be able to do it.
I was hoping that it would be more of a challenge, but no i can do it all in my gear that I transferred my toons to the ptr with, no one has more than 2 pieces of 232 t9 there, on live i have 3 toons with full t9, mostly 245.
For leveling this wont make a difference at all, same for doing new 5 mans.........basically tldr there is nothing left to gear up for, unless they announce another filler patch.