Good to see the Surface Pro 3 works out. I know someone in the manufacturing business that would like to recommend SP3 unitsfor the production floor due to its size and versatility.
There was some lag when I'm adding last parts in the assembly but as Im student I've never worked on device that didnt have any lag. So for me this small lag isnt a problem. @sharpcolorado with pen and onenote its really useful for making changes on sketches. Only problem is that Im constantly afraid of breaking it in workshop.
I, too, consistently run Solidworks on my SP3 and I love it. The ONLY thing it cannot really do is fine renderings with RealView Graphics because of the GPU. Other than that, for 3D modeling and a pretty decent amount of engineering, it is wonderfully adequate.
I also have the wireless version of 3D Connexion 3D mouse and it is fantastic.
My current best hack is to crimp the pen holder and put it on the kickstand. It presents the pen to you like a real pen holder at almost EVERY angle the kickstand gets set to (except when approaching fully back...then it gets a little akward), and folds flat when the kickstand is flat.
I know someone who is using quite a few CAD programs on their mix of SP2 and Sp3s. The only thing they have had a problem with is one Autodesk program that won't work because it requires a Quadro GPU. Most of those are primary business systems.