Today, NVIDIA not only launched the GTX 750 in this review, but also introduced the more powerful GTX 750 Ti based on the same architecture. I suggest you take a look at the GTX 750 Ti review to get all the details.
The GTX 750 non-Ti comes with 512 shaders instead of the 640 of the Ti, although clock speeds are the same. NVIDIA could unfortunately not provide their GTX 750 non-Ti reference design, so we can't judge the performance uplift of the out-of-the-box overclock by ASUS, but I suspect it to only be a few percent. The ASUS GTX 750 OC provides performance matching AMD's R7 260X and is 8% faster than the HD 7790 and GTX 650 Ti. The GTX 750 Ti is 14% faster, which is a pretty sizable difference. The GTX 650 Ti Boost is 23% faster and the R7 265 is even 31% faster, which clearly does not put the GTX 750 into a position to run 1080p games unless you want to cripple details settings. You might not have playable framerates in many of the latest titles at even 1600x900 with everything set to medium. Older engines or less demanding titles, like Diablo III or Batman: Arkham Origins, should run fine, though. Still, I'd be hard pressed to recommend these performance levels to a gamer who asks me for buying advice.
Power/heat/noise, on the other hand, are this card's forte. NVIDIA has improved power consumption of their new architecture, but I doubt anyone would have expected such a huge improvement. The new GPU is basically almost twice as efficient. However, when comparing the GTX 750 non-Ti to the GTX 750 Ti, we don't see the expected reduction in power consumption that should go along with the loss in performance. The out-of-the-box overclock by ASUS may have worked against them in that regard, or it could also be the board design. Still, the card is amazingly efficient, which makes it a great fit for any small form-factor or media-center PC. Noise levels of the card are also very good; I was actually a bit worried when I saw the ugly cooler, but ASUS did a good job with their fan settings. It is extremely quiet in idle and you'd be hard pressed to make the card out over components in your system while gaming. I only wish ASUS had designed the card as a single-slot or low-profile solution, which should have been easy given its power requirements.
Overclocking works very well and provides a good deal of extra performance. But it could have been even better would NVIDIA's power limiter not engage so quickly. Normally, you'd ramp up clocks until you'd come across stability issues, which won't happen with the GTX 750. The card will instead sense that its power limit has been exhausted and clock down. So the way to look for a good overclock is to increase the frequency in steps until you see a drop in actual gaming performance.
NVIDIA's MSRP for the GTX 750 non-Ti is $119 and ASUS adds another $20 price premium for their custom OC version. I find both price tags to be quite steep, even with the amazing power consumption considered. The GTX 650 at $100 is a much better deal and the GTX 650 Ti Boost was only $130 before it was pulled off the market, and it came with much better performance and was also very quiet. If you think of yourself as a serious gamer, you should really save up a bit more to be able to purchase a card that provides better framerates. Yet a casual gamer with lots of web browsing and productivity could opt to look at the GTX 750 as an interesting option because of its incredibly low noise levels and power efficient operation.