UA > Ruin until you have enough either enough crit to make Ruin worth it or enough +Spell to make Shadow and Flame + Ruin worth it (which you did not go into Destro fully enough to get SnF.
In other words, I wouldn't suggest it.
You will find that you perform much better in Pickup 5-mans - although you'll also find yourself pulling a lot more agro. UA is far superior for standard PVP as well, as it adds an element of restraint and confusion while simultaniously adding more damage.
Demonology harks on 2 strengths: superiority over a single target by use of teamwork (generally Felguard + Warlock), and enhanced simple damage output and mitigation through talents such as Demonic Knowledge, Demonic Tactics, Master Demonologist, Soul Link, ect. You will find that, even as Affliction, you will be constrained to single targets in Outlands until you start to pick up some tBC Spells and gear, as the monsters out there are much gnarlier. For this reason, a Demonology build can be very nice to work with from about 58-65.
I definatly wouldn't rule out that option (well, any option really), but I assure you Affliction is still a viable way to go.