roight! so I messed around in SM cath yesterday with my warlock to see how effective it was using him
I have probably the crappiest gear out there atm so this was going to be interesting from the start.. 420 spelldamage around 6.5k mana and 7.5k hp.
I pretty much dinged him 70 and then left him whilst i did other stuff

at first I tried the VW thing, sent him round the courtyard collecting all the mobs, seems to work quite well tbh. SOC 3 times and 90% of the mobs die
moved up to the fountain same again, altho sometimes i had to cut the pulls short due to low hp on my VW :S
When i got the the room however my VW died cos i was being silly and i forgot to go shard farming before going through SM.
So i whipped out my imp and wanted to see what i could do without a pet.

I started by attacking small clusters of mobs with SoC and then moving on to the boss once i had cleared it all..
this was taking too long tho .. so i decided to try taking on larger groups
needless to say after a few wipes trying to go for too much I got the SM catch (inside the cathedral itself) down to 2 pulls with a 60% success rate.
I have now respected destruction, and should now be able to benefit a lot from shadowfury to aid me with this pull. (range might be a problem tho)
I can see it being very easy with a VW tho
For instances where mobs are more spread out I would suggest the 'old dot em up' technique. Affliction all the way here
Dot mania
One final point to using SoC on a warlock, for this kind of grinding regardless of instance. take off some of you spelldamage gear.. I know this sounds rly rly silly, but bear with me

SoC triggers after a certain amount of damage has been caused to your target. taking off spelldamage gear allows you to cast more SoCs before the first one goes off, which means you should be able to get a bigger BOOM! effect when they go off. I am not 100% sure on this but as I understand it ur spelldamage added to each SoC hit is reduced by a factor depending on the number of mobs/players hit by it, thus reducing your spelldamage should not affect the overall damage you caused (much )