Here's a close-up of the CrossFire connectors. The latest drop of Catalyst drivers bring multi-GPU (three- and four-card, specifically) speed-up for OpenGL applications, as well as across-the-board gains in popular games.
Card-comparison time. The Radeon HD 4850's PCB is slightly larger than the HD 3870's.
And it looks suspiciously akin to a reference Radeon HD 3850, albeit with an upgraded cooler and chunkier heatsinks on the power-regulation components.