The technical service people finally turned up after 1 week after numerous calls (supposed to be next day business service) and sure enough the fan of the Geforce 960 was blocked by a cable. (I had been instructed NOT to take the box apart otherwise I risked voiding the warranty.)
The technican took it apart replaced the card , "just in case", restarted. This time we could hear a fan rubbing on the cable. Best evidence of the actual problem. Took it apart again and all i can say is that he had problems putting humpty dumpty together.Finally restarted and temperatures no longer exceed 90 Centigrade with frame rates as expected.
I want to point out another issue that occurred. I asked the technician to put the PC through the Dell stress test for the video card (from their website) but every time we tried the PC locked up and required a hard reboot. Now I have tried that stress test before without issue when we were testing the unit on another day and no lockups. I researched the board and sure enough these Skylake boards are prone to CPU lock up when stressed. Downloaded one of the those free stress tests and the system is humming nicely again, no sign of lockups.
Personally, I still think that the X51 as designed is way too hot compared with an ugly big box with big fans and airflow and I don't see it having the longevity of an equivalent system in a cooler environment.
Glad you got your problem solved!
I think the X51 is perfectly fine. I have asked several Dell (Alienware) Techs if opening the case would in-fact void my warranty, each one said "No". However, I don't own an Alienware X51 (yet), but I assume that they would only tell you this with a problem of theirs..for example the cable rubbing against the GPU intake fan. I know there are several people here that could have walked you through your issue, I'm almost certain your GTX 960 was not faulty at all and the ONLY issue was the cable. However, if you aren't too familiar with working on PCs then it's understandable.
If anything ever happens with your X51 and you don't feel like dealing with a weeks worth of phone calls or chat attempts, come here again and I will be willing to help you. Just because it's an Alienware doesn't mean it isn't the same as any other PC (Besides Alien command center software).
Again, glad you got your problem solved!