They both are in the same class of GPU performance, with the 7730M does offer something newer, or expansion as I see
Here's the technical review from notebookcheck ...
"The AMD Radeon HD 7730M is a DirectX 11 graphics card for medium sized laptops and positioned in the performance class. It is manufactured in 28nm and based on the GCN (Graphics Core Next) architecture.
The Radeon HD 7730M is not yet officially announced and therefore the information is still based on rumors and leaks.
The design of the Radeon 7700M series has its roots to the Cape Verde chip as found, for example, on the desktop Radeon HD 7750 with 512 1D shader cores and 32 texture units. However, it has a core clock of only 575 - 675 MHz compared to 800 MHz for the HD 7750. As a result, power consumption is expected to be much lower. While the desktop-version supports PCIe 3.0, the 7700M-Series doesn't (according to AMD).
The performance slightly below the DDR3 version of the GeForce GT 640M. Therefore, current (Spring 2012) and demanding games run fluently in medium or high settings in most cases.
Features of the 7730M include the new UVD3 video decoder for decoding MPEG-4 AVC/H.264, VC-1, MPEG-2, Flash and now also Multi-View Codec (MVC) and MPEG-4 part 2 (DivX, xVid) HD videos directly from the AMD GPU.
The 7700M series also supports automatic graphics switching between the integrated GPU and discrete GPU. Called Enduro, the technology supersedes AMD's Dynamic Switchable Graphics and is similar to Nvidia's Optimus. Furthermore, the 7730M can directly support up to 6 connected monitors using Eyefinity Technology if Enduro is disabled.
Other features of the 7700M series include ZeroCore for reducing power consumption when the display is turned off and Power Gating to power down areas of the chip that are not used. PowerTune allows automatic overclocking and underclocking of the graphics card as long as the GPU is within its TDP range. For example, the chip may be underclocked when running FurMark and OCCT, but will overclock in certain games like Lost Planet, Crysis or Resident Evil 5.
The integrated HD audio processor is able to transmit HD Audio (TrueHD or DTS Master Audio) over HDMI and DisplayPort (e.g., for Blu-Ray videos). Additionally, it now allows audio to output simultaneously and in parallel to multiple devices with the new Discrete Digital Multipoint Audio (DDMA) feature.
Power consumption of the 7730M is suited for 15-inch-laptops or greater."
7670M ...
The AMD Radeon HD 7670M is a middle class graphics card for laptops and based on the same chip as the Radeon HD 6650M. Therefore, it supports DirectX11 and is still manufactured in 40nm. According to AMD there are two versions available, a slower clocked Thames-Pro with GDDR5 memory and a faster clocked Thames-XT with DDR4 memory.
The 480 Stream processors should be still based on the "old" 5D architecture similar to the 5000 series. Therefore, the number of shaders is not comparable to the 1D cores of current Nvidia GPUs. The Tessellation performance should be improved (like the desktop 6800 series) with the new cards. The Stream processors can be used with DirectX 11, OpenGL 4.1, DirectCompute 11 and OpenCL. With the later two the cores can also be used for general computations like transcoding videos.
The 3D performance should be identical to the Radeon HD 6650M. However, in our benchmarks the card positioned itself sometimes even on a level of the higher clocked Radeon HD 6730M (same chip). Keep in mind that different driver versions and CPUs may also impact the benchmarks. However, demanding games of 2011 like Battlefield 3 only run fluently in medium detail settings. See at the end of this page for detailed gaming benchmarks. Compared to the competitor, the 7670M positions itself in our tests slightly above the GeForce GT 630M on a level of the GeForce GT 550M.
The new UVD3 video decoder supports the decoding of MPEG-4 AVC/H.264, VC-1, MPEG-2, Flash and now also Multi-View Codec (MVC) and MPEG-4 part 2 (DivX, xVid) HD videos on the graphics card.
Furthermore, the HD 6600M series integrates a HD audio controller to transmit HD audio (TrueHD or DTS Master Audio) over HDMI and DisplayPort (e.g. for Blu-Ray videos).
The AMD HD3D Technology offers support for Blu-Ray 3D and 3D displays (integrated and external). However, the solution is not as mature as Nvidias 3D Vision.
Thanks to Eyefinity the graphics chip is able to theoretically drive up to 5 monitors simultaneously. However, this only works if the laptop features enough DisplayPort outputs.
The power consumption of the chip should be similar to the Mobility Radeon HD 5650 and therefore suited for 15" laptops and up.
cheers ...
