Also, as a professional computer builder, I took a look at the specs you posted for your current machine. Yes, it IS time you upgraded, given your work in ZBrush and Rhino. Also, from looking at the componenets, this looks to be a USA machine. If that is correct, and you are living in the USA, then I'd add some additional recommendations.
This looks to be a desktop, rather than a laptop. If you are comfortable with a desktop, I would recommend you replace your current desktop with another desktop, rather than a laptop. In general, a desktop will last longer, and is easier to upgrade in the future. For the most part, a desktop has better air circulation, and better cooling options for the CPU, video card and for the RAM, than does a laptop. So, because it is able to keep the components coolor, all the components last longer. Plus, the coolor the components, the better they perform. Heat is the Number 1 killer of computers. However, if you have a particular need for a laptop, feel free to ignore this idea.
Second, if you purchase something like a dsktop machine from iBuyPower, you can upgrade almost any of the components in the future as your needs change or as changes occur in the technology. (The primary reason that I always build my own machines.) , So, an upgradeable desktop will save you a lot of money over the long-term. Laptops, especially like those from iBuyPower can be upgraded, but it is more difficult to upgrade them.)
An iBuyPower type of machine works well in your particular case, because you can probably salvage the Windows OS, the Western Digital hard drive, and the Sandisk SSD from your old machine and put them into a new desktop. In fact, if it were me, I would specify an iBuyPower desktop - most come without a hard drive, and plan on putting in your own hard drive and SSD into it. Of sourse, you can also add your optical drive as well. (If you're not comfortable with working in the guts of a computer box, I'll volunteer to help.)
I would not give any consideration to trying to salvage your existing RAM, as DDR3 is significantly obsolete now. In fact, you probably could upgrade your existing box a bit with a more powerful CPU and video card --- and save some money, but the DDR 3 RAM this motherboard requires wil be a strong limiiting factor, and you won't gain much. So, I think you have the right idea in going for a more modern motherboard, with better throughput speed, more powerful RAM and CPU combinations, and the ability to host one of the new generation nVidia video cards. Of course, another option for you is to salvage just your hard drive out of your existing box, and put everything else up for sale on Craig's List or the equivalent. You'd probably get some reasonable amount of money for it. But, keep your hard drive. Even if you go for a box with a solid state drive for you main C: drive, you can take the load off you computer by using the salvaged hard drive as a "D:DATA" drive and write all you working data to that second drive.