Take a look at yourself on MrRobot. You can see the stat comparisons as you intentional swap out different pieces.
Fire Mage in WoW
For me personally, I always go for set bonus.
As a Fire/Frost Mage, its very important to have your 2 & 4 set.
Cheers guys, I will give it a run using the lfr 2 set and see if I get better numbers
With 2p bonus it lines up nice with alter time and PoM. and with 4p you get them at off time making it harder to get those high combustions. Also on most fights you will make maybe 1 more Combustion witht he 4p bonus. that is using on CD to benefit from bonus. if you go for bigger numbers you will probably not see any more combustions.