Instead of XPSs, we bought Precisions 15 5000 at work [1]. They are basically XPS 15, (virtually indistinguishable apart for the engraving on the bottom), but you can spec them to bits (you can even get a Xeon processor if you want,have them with no OS / Ubuntu). All of us are reasonably happy with them.
[1]: http://www.dell.com/uk/business/p/precision-m5510-workstatio...