Jonathan,
I have a pair of Westone UM2 IEMs. Dual drivers. I picked them up when they were discontinued for a very reasonable price. They are certainly not "top of the line". As you know, I both play guitar and do a lot of lead vocals. I've never tried three driver IEMS, so take this into consideration in weighing my opinion. (I know there are several here at the club that have a lot more experience with IEMs).
That said, from my view my dual driver IEMs are far superior to floor monitors. I suspect it is the law of diminishing returns - the jump from floor monitors to dual drivers is far greater than the jump from dual drivers to triple drivers. More important is getting everything miked and mixed. And I love that my Mackie DL32R allows everyone to control their own IEM mix independent from anyone else. Now if I could only get everyone in the band to embrace IEMs!
As a bonus, I always bring my IEMs with me when I fly. They are very effective at blocking out the airplane drone and, of course, sound great as earphones.
Bill, tgo