43 is NO problem at all:

around 40-41, Tanaris! kill bandits, pirates and nameds. If you get the robot chicken to drop (home robot wooshie), you can do the escort aswell. collect wastewander waterskins or whatever they are called, and IF you get 25 of them, accep the quest in Gadget and turn it in. Else skip that part.

43ish - Searing Gorge: kill lava spiders, golems and whatnot - there is also the named underground, incendosaurs and the outhouse quest - bring 3 silk on each of your toons. Dont go for the "outhouse key" quest, because if it drops, only 1 drops at a time and it takes ages to get 4 more. You can always save them, distributing them to alts while doing the other quests, and if you are lucky to get all 5, then ofc do that turnin aswell. SKIP "Ledger from Tanaris" and all other collection quests ofc.

45 - Hinterlands, woohoo

47-48 - back to Tanaris, kill ogres and do the Noggenfogger things

48+ cherry pick killquests from Azshara (and the amazing tablet quest), southern felwood and blasted lands.

50+ WPL: entry, and then do the cauldron quests, picking up the quests at each field and do those aswell - WPL is TONS of killquests. Hit EPL around 54

basicly, use http://www.wowhead.com/?zones#0+2+1 and just jump around to each area as soon as you can, cherrypick killquests and you'll be blasting to 60.