TrustedReviews has posted a review of the Sapphire Radeon X550 graphics card

This X550 from Sapphire has 256MB of memory, with 128-bit memory bandwidth. It runs with a 400MHz core and 250MHz (500MHz effective) memory. It is fairly obvious, that the X550 is little more than a speed bump of the X300, bringing it closer to the speed and specifications of
the X600.

Sapphire Radeon X550 Review