I am having the exact same issue with my SP7 i5 256gb. The interesting thing is that I don't think the computer is actually freezing its the display that is freezing. When I have a second monitor connected through the surface dock the mouse pointer and keyboard keep working on the second monitor but will freeze on the SP7 screen. Its very strange. I can even touch the SP 7 Screen and it will move on the second monitor but not the SP screen. Actually as I am typing this right now, what I typed stopped updating on the SP7 screen up at "its very strange" but I am still typing on the surface keyboard and its updating on my second monitor with no lags. After about 10 -20 seconds the SP7 screen will catch up. I will probably try exchange it at Best Buy tomorrow.
Update. I exchanged mine for a replacement which has been working flawlessly. It definitely was a hardware problem.