Papuz, if you don't need the higher-speed CAD support of Quadro graphics processors, I'd go with a Geforce graphics processor in any new laptop. Same hardware as a Quadro, but lacks higher-speed CAD support for OpenGL in firmware/driver (Geforce instead uses slower OpenGL support built into Windows), but for over $1,000 less for high-end processors. For example, I bought a new 17" laptop with the same speed as the highest-end M6700 for non-CAD applications, from the same company, with the same warranties, but for 1/3 the price.
In any case, don't swap graphics processors without having experience doing such things, or you could lose whatever you spend on the replacement 3700M. Don't update to any vBIOS besides the versions we've listed, or else you may lose the ability to use the replacement 3700M in your W700. Clean out the tiny air intake vents in the bottom of the W700 under the two fans, or else you'll burn out the replacement 3700M. Also clean out the air outlet vents in the sides/rear of the laptop. Users HAVE gotten the HP cards to drive BOTH internal displays on the W700ds. If you fix/keep your W700, I recommend running it on a Cooler Master NotePal U3 Laptop Cooling Pad with Three Configurable 80mm Fans (R9-NBC-8PCK-GP), centering a fan under each of the two W700 fans, with the cooler set to max cooling, to help preserve the 3700M. Keep your data on the machine backed up to external media in case of failure.
Personally, I'd just buy a new 17" laptop. The W700 is already 4+ years old, new 17" laptops are much faster, they hold 4x more memory, SATA3 is much faster than the W700's SATA2, USB 3 is much faster than the W700's USB 2, displays are now available that are much better (although they're 1920x1080 instead of 1920x1200), external tablets are much better than the W700's internal tablet, you'll get better software/driver support with a new machine, and it costs more time/money to rely on any laptop that's out of warranty.
But, whatever you do, good luck!