biggest issue I see is that you should have much more RAM
Not sure I agree with that - not with a starting point of 4Gb. While I do feel 8Gb of RAM is the sweet spot for Windows 7, 4Gb is nothing to sneeze at - not when the graphics solution has its own dedicated RAM. Also, we don't know if these systems have 32-bit or 64-bit Windows and 8Gb is a waste unless 64-bit. Plus, that does not answer the OP's question.
If 64-bit is an option, then certainly going with 8Gb of RAM would be good, if possible - but not a necessity. And if 64-bit is an option, then I recommend that even if sticking with 4G of RAM as 64-bit Windows 7 (1) has more security features than its 32-bit sibling and (2) a 64-bit OS will utilize the full 4Gb better.
Do you think one of these two are far superior/absolutely more powerful because of the changes seen in bold? Or does the second one which has a higher number of specs not matter much compared to the first?
more powerful"? No. But I think it would be noticeable in a side-by-side comparison with the 6750M with 512MB GDDR5 graphics notebook doing better. And while the 200MHz advantage for the CPU may not seem like much, it does mean graphics tasks can be handed off to the GPU that much faster - and that cannot hurt over all performance.
Note that a graphics card that is best suited for CAD/CAE, graphics design and video editing is NOT the best card for games - and vice versa. CAD/CAE, design and editing are best with a "workstation" graphics card and as can be seen here
can cost many times more than a good gaming card.
But if the jump up helps video editing wise, or during playback of movies to watch than yes I'm concerned.
It takes very little horsepower to play
tunes, or movies from a network, HD, DVD or BluRay. It takes RAM and 4Gb is plenty for that, and it takes free disk space, and in the case of streaming, a good network connection.
Video editing is a different animal and for that, you want the best your money can buy.
If the price between the two is not ridiculous, and the faster system is still within budget, go for the faster one.
Lastly does anyone know if you can upgrade memory on laptop graphics cards?
I am not aware of ANY graphic solution (whether notebook or PC) where you can upgrade the graphics memeory. On a PC, if you want more graphics RAM, you buy a new graphics card that is populated with more graphics RAM. For notebooks, with very few exceptions, the graphics solution is totally integrated and cannot be upgraded at all. This is because, despite what notebook marketing weenies would have us believe, notebooks are NOT desktop replacements and do not make good gaming machines. Notebooks are designed to be thin and lightweight for road warriors and PowerPoint presentations. Their lightweight, compact design does not allow for sockets and expansion slots to add or upgrade components. Note that even full tower cases are challenged to provide adequate cooling for serious gaming, so there is no way a tiny notebook case with limited fan and ventilation support can. Plus, notebooks are nearly impossible for the normal user to open up and expose the interior for a thorough cleaning of heat trapping dust. So coupled with limited cooling capacity to start, and then with the inevitable build up of heat trapping dust, notebooks, with their mobile CPUs, routinely toggle down in speed to reduce heat (and conserve battery runtime).
I do agree with Rusbel on his comments about using an SSD (which is ideal for page files, BTW - at least the latest generation SSDs are). I also feel that an i7 in a notebook maybe a bit much - unless the budget is not really a concern. You might look at a nice i5 with 8Gb of RAM, good graphics (perhaps one with 1Gb of graphics RAM) and perhaps a SSD.