Here are the technical specs.

514 million transistors on 55nm fabrication process
PCI Express 2.0 x16 bus interface
GDDR3/DDR3/DDR2 memory interface (depending on model)
Microsoft® DirectX® 10.1 support
Shader Model 4.1
32-bit floating point texture filtering
Indexed cube map arrays
Independent blend modes per render target
Pixel coverage sample masking
Read/write multi-sample surfaces with shaders
Gather4 texture fetching
Unified Superscalar Shader Architecture
320 stream processing units
Dynamic load balancing and resource allocation for vertex, geometry, and pixel shaders
Common instruction set and texture unit access supported for all types of shaders
Dedicated branch execution units and texture address processors
128-bit floating point precision for all operations
Command processor for reduced CPU overhead
Shader instruction and constant caches
Up to 128 texture fetches per clock cycle
Up to 128 textures per pixel
Fully associative multi-level texture cache design
DXTC and 3Dc+ texture compression
High resolution texture support (up to 8192 x 8192)
Fully associative texture Z/stencil cache designs
Double-sided hierarchical Z/stencil buffer
Early Z test and Fast Z Clear
Lossless Z & stencil compression (up to 128:1)
Lossless color compression (up to 8:1)
8 render targets (MRTs) with anti-aliasing support
Physics processing support
Dynamic Geometry Acceleration
High performance vertex cache
Programmable tessellation unit
Accelerated geometry shader path for geometry amplification
Memory read/write cache for superior stream output performance
Anti-aliasing features
Multi-sample anti-aliasing (2, 4 or 8 samples per pixel)
Up to 24x Custom Filter Anti-Aliasing (CFAA) for superior quality
Adaptive super-sampling and multi-sampling
Gamma correct
Super AA (ATI CrossFireX™ configurations only)
All anti-aliasing features compatible with HDR rendering
Texture filtering features
2x/4x/8x/16x high quality adaptive anisotropic filtering modes (up to 128 taps per pixel)

Starting things off with Crysis we see the 4670 perform quite well at 39.1fps. Here we see that unfortunately Crossfire is not supported for the 4670 cards at least in the driver revision have. Hopefully those are updated soon.

UT3 shows different results with Crossfire and tops all other cards including the 9600 GT. When optimized the 4670 cards definitely seem to be formidable in Crossfire.