Legit Reviews posted a review on the ASUS GeForce GTX 680 & GTX 670 DirectCU II Top Edition Video Card

Gamers that have the ability to spend over $350 on a graphics card have a number of cards to pick from as both AMD and NVIDIA have released great high-end videos over the past year If you are a fan of NVIDIA it doesn't get any better than the GeForce GTX 680 and GeForce GTX 670! Both of these cards share the NVIDIA GK104 'Kepler' GPU and represent the best of what NVIDIA can offer the single GPU desktop market. These are are ideal for those that game at 1920x1080 or higher with all the image quality settings cranked up. If you want to play a game and see it as designers intended, then these should be be the ones you are looking into.
GTX680 Specs

Just in case you need a reminder, here is a quick table that shows the differences between the GTX680 and GTX670. The GeForce GTX 680 has four Graphics Processing Clusters (GPCs) with a total of eight Streaming Multiprocessor (SMX) units, which is good for an impressive 1536 CUDA Cores and 128 texture units. The base clock speed of the GeForce GTX 680 is 1006MHz and the typical Boost clock speed is 1058MHz. The memory subsystem of the GeForce GTX 680 consists of four 64-bit memory controllers (256-bit) with 2GB of GDDR5 memory.

For those looking to save a buck, the NVIDIA GeForce GTX 670 has the same core with some functionality disabled and lower clock speeds on the CUDA cores. To be specific this card has just 7 Streaming Multiprocessor (SMX) units, which means it has only 1,344 CUDA parallel processing cores and 112 texture units. The base clock speed of the GeForce GTX 670 is 915MHz and the typical Boost clock speed is 980MHz. The memory remains the same, so you you still have 2GB of GDDR5 video memory, running at 6,008MHz over a 256-bit memory interfaces to seal the deal.

  ASUS GeForce GTX 680 & GTX 670 DirectCU II Top Edition Video Card Reviews