I agree, I wouldn't saw off original cooler unless there is any other way.
With S1 you get one longer heatsink, used for X800 cards VRMs I think. Looks same like memory ones, but is about the length of 5-6 memory heatsinks combined. I have no access to 4850 for now, but I think it can be sawn in two parts, and should cover whole VRM area on the card. You'll just need something to stick it on with (either Arctic Silver or any paste plus a bit of glue perhaps?). Though that HS has holes, but I doubt they'll match 4850's :/
EDIT: Unless someone has both 4850 and this HS with S1, I can take a measure of HS and holes, and one of you can check if it would fit on 4850, or if maybe even holes match. Will be posting picture/dimensions in a few minutes, just have to get my camera
EDIT2: 9.4cm length x 2cm width, and holes are 8.9 appart;middle part that would lay on VRMs is 9mm wide.
http://www.imagehosting.com/out.php/...030464crop.jpg http://www.imagehosting.com/out.php/...030460crop.jpg