You shouldn't and can't compare the 2, if you're speaking of the m17x R3. If you're talking about the m17x R2 then speak away. But for my short statement I'll assume you're talking about the R3 system. And the reason why I say you can't compare the 2 is because the R3 system takes us back to the Dell XPS M1710 one of the most beloved XPS systems to date. The R3 system reminds me alot of that system but even better. The m17x R3 gives you about a 4 hour battery life on integrated gpu and has a single 6970 which is pretty powerful while still being roughly 9lbs which is a great size and form factor for a 17 inch system. The m18x provides little if no portability what-so-ever, on top of that it's made of metal which is nice but it adds to the weight and let's be honest after you throw in your 330 PSU you're not really taking this thing anywhere and I'd hate to think of the individual who is taking this thing everywhere he goes and makes good use of it's Metal Frame as he drops it over and over again. The m18x offers you a DUAL GPU setup and a larger screen but completely restricts any movement being done with it. Don't get me wrong, you can move it around, you just don't want to take with you everywhere you go.