is there any sort of mod that we can do to increase available Power draw on the 4850???

The 4850 supports a max draw of 150W, 75w on the 6pin, and 75w on the PEG.
The 4870 supports a max draw of 225W, 150w on the double 6pins, and 75w on the PEG......

If ATI puts two connectors on @ 750MHz core + DDR5, that is telling you something right there already. We are running 900~MHz on a single connector