But really, chanks, you will not be sorry for having the m17xr3 it is a beast machine in itself.
I was halfway thinking about the m18x when i was looking at getting mine and i was thinking i really dont need that much of a bigger laptop; i was even considering getting the m15x at the time too; but landed on the m17x. and i love it. i mean there are a few differences as what can be done, but i know i'm not regretting the m17x. and neither should you.
Plus you can always upgrade some as well as needed, which shouldn't be for a while.
Don't be too worried about it; the first release of the M18x had a terrible issue with it's option of Radeon HD 6970s, if that makes you feel better (my cousin was one of those people who had to deal with it). The M17x is still a wicked machine, you have no need to feel envious, haha! Just be happy that you don't have to lug around a 24lb laptop!
I first bought an M11x. Loved its portability and size! Eventually, I got an M17x R3 and let me tell you. There are times that I wish I had and was using the M11x! Like when I'm just lying on the bed, lying down on the couch watching tv, while on the train, or any situation where there is limited space.