IMO Affliction=TrueWarlock...demo is a pokemaster and destro is a shadow mage.

I leveled Affliction from 1-70 and remain Affliction but did try out demo on the PTR once...I was gd healing my felguard more than I was doing damage.

While leveling I played a game in my 40's in Tanaris (solo) with imp out and would see how many concurrent mobs I could take on at once. By using fear, instant howl of terror and drain tanking using drain life I could easily manage 5 mobs and I believe it was before Siphon Life talent was in the game.

With 5 locks now I would definitely still go Affliction, have 1 go Instant corruption then enough demo to get 3/3 imp void walker then go back into the Affliction tree. Use VW on 1 to tank a mob (imp VW has awesome tank abilities and great damage mitigation) and I would use the imps on the other 4 locks, leave 1 phase shifted so he never dies to keep your blood pact up in case things go bad. With 5x dots and maybe a finishing 5x shadow bolt I doubt the improved vw would lose aggro most of the time on same level or 1-2 level higher mobs.

Questing would be very easy but yeah instances might be rough with 5x locks. Maybe you could team up with a tank and healer and take 3 locks at a time into instances?

Plus 5x drain life and drain souls look so cool.