According to TheInquirer, the two derivatives are code-named RV630 and RV610. They're both based on 65nm process technology and scheduled for launch in May. The RV630 will reportedly see the light of day in two flavors, dubbed Radeon X2600 XT and Radeon X2600 Pro. Aimed at the $200 price point, the XT is said to have 64 shader processors, a 650MHz core clock speed, 256MB of 800MHz GDDR3 memory, and a 128-bit memory bus. As for the Pro variant, it'll supposedly cost $150 and sport 550MHz core and 700MHz memory speeds.

Moving down to the RV610, The Inq says that GPU will launch in three variants: a $100 Radeon X2300 XT, a $70-80 Radeon X2300 Pro, and a $60 Radeon X2300 LE. The top-of-the-line Radeon X2300XT is clocked at 650MHz and has the memory ticking away at 1400MHz. The card uses GDDR3 memory with a 128-bit memory controller and has 32 Shader units. It is another 65 nanometre chip and the card will sell for $100. Next up is the Radeon X2300PRO with 500MHz core and 1400MHz GDDR3 memory with 128-bit memory controller. It has 32 Shader units, 65 nanometre and the 256MB version will sell for $80 while the 128Mbyter should sell for $70.  The last in this DirectX 10 mainstream and low-end, unified Shader line-up is the Radeon X2300LE. This card will end up clocked at 500MHz core and 800MHz memory. It uses 128MB of 128-bit GDDR 2 memory and will have 32 Shader units. The chip is 65nm, very low power consuming and will sell for around $60. A Direct X 10 card for $60 sounds like a nice bargain for Vista.

Even if this info is currently correct, getting exact info on core and memory clock speeds today for cards that launch in May is, of course, a tricky business. Plans could, and probably will, change somewhat between now and then. But it wouldn't surprise me if half of that is true :-)