1.ATI Radeon™ HD 4870
*956 million transistors on 55nm *fabrication process.
*PCI Express 2.0 x16 bus interface.
*256-bit GDDR3/4/5 memory interface.
*Microsoft® DirectX® 10.1 support.
*Anti-aliasing features:
-Multi-sample anti-aliasing (2, 4, or 8 samples per pixel)
-Up to 24x Custom Filter.
Anti-Aliasing(CFAA) for improved quality
-Adaptive super-sampling and multisampling.
-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).
-128bit floating point HDR texture filtering.
-sRGB filtering (gamma/degamma)
-Percentage Closer Filtering (PCF)
-Depth & stencil texture (DST) format support.
-Shared exponent HDR (RGBE 9:9:9:5) texture format support.
*OpenGL 2.1 support.
*ATI CrossFireX™ Multi-GPU Technology
-Scale up rendering performance and image quality with two, three, or four GPUs.
-Integrated compositing engine.
-High performance dual channel bridge interconnect.

2.ATI Radeon™ HD 4850
*956 million transistors on 55nm fabrication process.
*PCI Express 2.0 x16 bus interface.
*256-bit GDDR3/4/5 memory interface.
*Microsoft® DirectX® 10.1 support.
*Anti-aliasing features:
-Multi-sample anti-aliasing (2, 4, or 8 samples per pixel).
-Up to 24x Custom Filter Anti-Aliasing (CFAA) for improved 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).
-128bit floating point HDR texture filtering.
-sRGB filtering (gamma/degamma).
-Percentage Closer Filtering (PCF).
-Depth & stencil texture (DST) format support.
-Shared exponent HDR (RGBE 9:9:9:5) texture format support.
*OpenGL 2.1 support.
*ATI CrossFireX™ Multi-GPU Technology:
-Scale up rendering performance and image quality with two, three, or four GPUs.
-Integrated compositing engine.
-High performance dual channel bridge interconnect.

Ref = (http://ati.amd.com/products/Radeonhd4800/specs.html)