When I was shopping around for 7's, I played a used M-107, and there shouldn't be any differences in the
neck dimensions, just other options (pickups, trem) with the M-207's, right?
Anyway, the M-107 was cool looking (flat black) and sounded decent, but it felt absolutely huge in my hands; literally like trying to play a 2x4 piece of lumber (and I'd say I have medium to large hands -- no problems with most stretches). Granted, I've grown used to
Ibanez necks (my ESP M-202 6-string feels pretty big compared to my RG470, but the ESP is flat/thin so it's not bad and I like the EMG pickups), but I could tell after about 30 seconds of playing the M-107 that I was either going to have to find a smaller/better neck or forget about buying a 7-string due to it feeling so uncomfortable.
That's about the time the RG 1527's were first being talked about, and everything after that I heard was pretty positive so I took a chance and ordered one. I can honestly say I've never been happier with a guitar -- it sounds and feels great. The neck on my 1527 feels only slightly wider than the neck on my ESP M-202 6-string! The transition from 6 to 7 strings was not a problem for me with my 1527.
My 1527 has great fretwork, no buzz at the low end, and if you use the trem at all then you gotta go Ibanez -- the most disappointing thing about my ESP is the cheap Floyd imitation (feels stiff, has very limited range of motion, won't flutter no matter how you adjust it or how many springs are attached, I can't stand the arm, etc., etc., etc.!)
Anyway, I know this is just one guy's opinion, but having owned both Ibanez and ESP 6-strings, and having played an ESP 7-string and bought an Ibanez RG1527, I figured I might be able to give you a helpful perspective. Good luck either way, hope you find an axe that sounds and feels great for your needs.
EDIT: One more thing -- regardless of what you buy, be -SURE- to set enough money aside to take it somewhere and have a good setup done (unless you can do this yourself), because even an RG1527 prestige neck that's done right from the factory will probably need some TLC after being boxed up and shipped.
