I'm a pro musician, and gig playing drums at least a couple of times a month.
I've used Sennheiser CX300, UE Super Fi 5, UE700, and various cans including Sennheiser 280PRO.
I would say that isolation was very poor with CX30, and UE700.
It's slightly better with UE super fi 5 and the cans. The other important thing is comfort - the wire from full size headphones comes down the side usually, and it's a pain, getting caught in one arm all the time. IEMs, with wire going down my back are more comfortable.
Also, with cans, they tend to shift with movement, IEM's are a bit better at staying in place. With IEM's, I don't feel like I'm wearing something extra. Cans always feel bulky and a bit silly.
If you take drumming seriously, I would recommend custom IEMs - the best isolation and comfort.
My son is a drummer (+ I'm a long-time musician), and I would probably lean you toward the Etymotic stuff -- MC5 (cheaper), HF5 (more expensive, better sound) or the ER4 Series (best). With the triple-flange ear tips, the isolation is wonderful! I've also used them as in-ear monitors for some on-stage show stuff, and they worked well.