Honestly, after looking at the perks I dropped 450 Eng on my DK's and pleveled JC up to 500. Here's the skinny:

You can't use ANY of the Engineering perks that get attached to your armor in arenas or rated BG's. No 18k shield on your belt, no Tazik Shocker on your gloves, no parachute cloak, no nitro boots. Period.

The Cogwheel sockets are just for the epic Eng helm. It's nice, but next tier there most likely won't be a new helm and you'll want to replace it.

That means for pvp Eng is basically the worst profession right now. Sigh.