By default, the AMD cards (so I'm assuming also the NVIDIA cards) have a really weird fan curve, as in the fan sits at 18% until it gets to about 75C...
Perhaps the same is occuring here.
Download this:- Afterburner | MSI Gaming Series
It's primary purpose is as an overclocking tool... but you can use it to override the NVIDIA driver's control over the fan speed and set your own custom curve (same as EVGA precision really!).
you could also try slightly downclocking the GPU core and see if that helps. as has been previously mentioned, reference PCBs/reference coolers are generally a bit soggy when it comes to cooling (Hence why you end up seeing tonnes of different custom PCBs from MSI, XFX, Sapphire, EGVA, ASUS and the rest) with things like Twin frozr cooling and/or huge heat sinks and fans.
Bottom line is, GPUs will always run hot. my R9 270X will hit 80C running valley benchmark with a slight overclock on it. Point is though, it never goes ABOVE 80c, and R9s can operate at up to 90C reasonably safely as long as the VRMs stay cool (below 75C). Unless you've got some seriously optomised airflow and/or proper custom watercooling, you're going to see highish temps when gaming at high settings.
I've just checked on the GeForce site, and they state the maximum operating temperature is 98C. In terms of card safety and component safety, you're actually OK. Realistically though you might want to invest in a case with good airflow and a good bit of room beneath the GPU for the hot air exhaust into. also make sure that your case is actually exhausting the hot air and pulling in cool air, not just one or the other, or you'll end up with turbulence, hot spots and hot air pooling in the top of the case, raising the ambient temps.