OK folks. Posting here since none of the mages I consulted was able to provide a clue.
Main question expanded: I have a mage. It's ffb/arcane. It's ICC-ready gearwise. His arcane dps is about 700 points behind his ffb dps (single target). Why?
This is my mage:
The World of Warcraft Armory - Chaon @ Madoran - Profile
I've conducted several tests on dummies to compare ffb and arcane specs. In all cases I used no other buffs than molten armor and arcane intellect. No flasks, food or external buffs were present. All tests were done as "till oom" tests with using mana gems, mana potion, evocation etc, and repeated at least 3-4 times each to reduce randomness factor. I've tried both using and not using the cooldowns of trinkets/internal abilities for each spec.
In all the tests, ffb was giving out about 700 more dps than arcane; thats something like 4.2k ffb versus 3.5k arcane.
Now, things I'm already aware of:
1) YES, I was using molten armor (and not mage armor) for arcane spec. Being actually a dps buff (compared to typical magearmor setup) for arcane, at a cost of reduced effective mana pool; problem is, even with this buff arcane dps is way lower.
2) Haste>crit for arcane and my gear is somewhat FFB (crit) tuned. OK; I have 3 sp/spirit gems and 3 sp/crit gems atm that benefit crit and not haste. All other gems are pure 23sp gems. There's no other place to "tune" my gear towards haste. If I replace all 6 those gems (sp/spirit and sp/crit) with pure haste gems, I'd gain 120 haste while losing about 80-85 (counting socket bonuses) sp. Would trading 80 sp for 120 haste increase my dps by 1k? I'd bet my account password that it would not.
3) My FFB rotation is typical (w/o cooldowns): keep scorch up, keep LB up, spam FFB, hit pyro on proc.
4) Yes, I am aware that LB explosions do some damage to adjacent dummy and affect my "single target" score a little. Consider them being 3k on average (2k to 4k with crits) and 10 second duration, that's about 300 dps incorrectly added to the picture of a "single target" test - but that STILL does NOT account for 700 dps gap with arcane
5) My arcane rotation is typical (again w/o cooldowns): ABx4, if MB proc - hit arcane missiles/MB, if it doesn't, hit arcane barrage.
So, what do I do wrong? Specs? Rotation? Being unaware of some factors that inflate single target value of ffb? Anything else? I'm REALLY looking for you help here.
EDIT: OK, torment of the weak. It's 12% more damage, or about 400 more dps. Still nowhere near close to cover and surpass the gap of 700 dps I'm seeing - EVEN if the target in question would be always considered snared (this isn't true at all).