The workstations are not designed with gaming in mind, however, they will knock them out of the ballpark if configured properly.
I've been using the Z4xx series at home for gaming and everything else I've needed with little complaints.
I think the desiding factor is 'what are you going to be using this for most?'
You can buy these units without graphics cards as you won't be wanting a Quadro card for gaming and coding tasks won't care. However, depending on the design programs, the Quadro card may be what you want. (Quadro cards can be put into "game developer mode" which allows them to funciton as GForce cards... but Quadro's cost a lot more.)
That being said, GForce cards cannot be SLi'd in Workstations.
Have you looked into the Omen X if gaming is more your focus?