Yes it is 100% compatible.
Does Intel 4th Gen i5 4440 3.0Ghz 6mb Cache Socket 1150 is totally comaptible with G1 Sniper B5. It will be enough for gaming with a Sapphire R9 280X.
It should have no issue with an R9 280X and it's a great pair.
The i5-4440 is on the official CPU support list. i5s are some of the best CPUs out there for gaming, and should not bottleneck a 280X.