Dual Boxing ShadowPriest/Rogue Mage/Rogue(Quiet new to it)

Greetings, I'm quiet new to dual boxing. I've got two accounts with shadow priest and mage on one account and warrior and rogue on other. I bought keyclone, got one not that good computer and two monitors. I intend to dualbox having one account on one monitor another account on the second monitor. I've tried some dualboxing with level 1 characters but it laggs abit if I have 2 WoWs opend on both screen it laggs even more, so I will probablly hide one WoW behind the other but that dosent matter. Now, due to new expansion new things etc. I need to make sure if I can dual box since I have to buy wotlk and gamecard for the other account. So the question is can I dualbox any of these characters; Shadow Priest, Mage, Rogue(I also got 62 warlock, 62 shaman maybe dual box them to 70 and make some other combination?) Which two are the easiest to Dbox and fastest? Thanks for any answer. :)

bump ;/