chances are yes, the 985 is the same socket as the 805
but the 985 is 125W, whereas the 805 is 95W - so there is the possibility that the mobo doesn't support CPU with that high wattage.
can you tell us what model mobo you have? i can't find info on what parts are inside the DX 4300-11 (even on gateways own site)
EDIT:
although mobos that don't support full wattage CPU's do exist they're not common, so i'd say with 95% certainty that a 985 would work. but if you want to be 100% certain there is a 95W version of the 3.2GHz 955 (part # HDX955WFK4DGM)
EDIT #2:
it only supports 95W CPU (thanks boden). looks like the 955 i mentioned above is the best & fastest you could get.