Finally, Nvidia has a solid mid-range GPU based on Kepler architecture. While the GTX 560Ti was far from a poor performer, AMD had nearly free reign over the mid-range market with the HD7850, and the HD7870 for users wanting greater performance at higher resolutions.
With the launch of the GTX 660Ti Nvidia’s taken back a portion of that market, and is even encroaching on the HD7950, and indeed even its own GTX670. The reason this is possible is the 1344 CUDA cores the GTX 660Ti is constructed from – the same number as the GTX 670. The main difference between the two cores is memory bandwidth and overclocking headroom. It seems Nvidia has simply put aside GTX 670 cores with underperforming memory controllers, lowered their memory bandwidth and whacked them onto a GTX 660Ti PCB.
What does that mean? Well put simply it means we won’t be seeing huge benefits from overclocking the GTX 660Ti, partly because of the assumed binning methods (it’s already memory-bottlenecked at high resolutions), and more importantly because of the same PWM control Nvidia has employed on its other Kepler cores, making overclocks above 15 per cent difficult at times.
For anyone not aware of how these new cards operate under loads, ‘GPU Boost’ is essentially a technology designed to monitor card temperatures and power usage, and adjust the core clock in real time. This means a touch of extra performance and higher efficiency when left at factory settings, though it means the card quickly becomes unstable when high overclocks are attempted. For this very reason, we’d suggest sticking with the HD7870 for some mid-range overclocking, and even the GTX 670 should overclock a little better, given that it’s not a ‘side-binned’ chip like the GTX 660Ti.
Our Gainward sample tested here today comes with a base clock of 1006MHz and a ‘boost’ clock of 1084Mhz, which sits comfortably above the reference design (915MHz base and 993MHz boost). When overclocked we were able to hit around 1200Mhz Boost, and a ‘base clock’ of 1122MHz. Not bad, but still far from ideal given we had to add +26mv to the core as well as raise the ‘power control’ bar to 110 per cent, raising both power consumption and heat output.
We did attempt to overclock higher, just to find the limits of this card, but it seems to share the same fate as the GTX 680: once you hit a certain clock, due to the high fluctuation of voltage and core clock, instabilities are quickly revealed and the system inevitably locks up or crashes.
Given that the main and arguably only difference between the GTX 660Ti and GTX 670 is memory bandwidth, it is important when buying one of these cards (if it’s to be used on higher resolutions, or with high levels of AA) that you find a stable memory overclock. While it is difficult, and we wouldn’t expect much more than a final clock of around 6400MHz (effective), it should be enough to see the GTX 660Ti raise its memory bandwidth up from around 146GB/s to around 190GB/s, matching that of the GTX 670 despite the lower memory bus of 192-Bit.
We hear what you’re probably asking, and that is “is there no other difference between the ‘660Ti and the ‘670?” and the short answer would be... no. From what we can tell the average card will measure in at 9.5in, they are both powered via two 6-pin PCI connectors, both have around 170W maximum card power (depends on samples obviously), both have the same CUDA core count and even core clock on the reference design. Essentially the GTX 670 is now aimed at gamers with a nice 2560 x 1400 monitor, while the GTX 660Ti should be poised to replace the GTX 670 at all lower resolution builds.
If we look at the heat measurements of the Phantom tested today, we do see the GTX 660Ti isn’t a hot card; in fact it’s relatively cool given the performance. Expect idle temperatures of around 30C inside your PC tower; as our ambient air is 19C in our test labs and we have an open-air test bench, we always have slightly lower-than-average test readings.
Powering up our trustworthy Heroes of Newerth we checked boost clocks are working correctly (as power usage is generally low), check fan profiles are set as the heat slowly rises and most importantly of all, we can test what a light load on the GPU is likely to do to the thermals of the card. In the case of the GTX 660Ti Phantom, we only see temperatures rise to around 40C. Not bad when you consider the card is also boosting to 1084MHz at times, and running at an inaudible 20 per cent fan speed.
Loading up some more demanding titles shows that the card is capable of producing a fair amount of heat, with temperatures hitting 78C in Battlefield 3, with a slightly faster fan speed of 30 per cent. Still, this temperature is far from alarming, and is for all intents and purposes remarkably low given the performance of the card.