Just out of curiosity I found a work around to get my wifi working on N. First turn on airplane mode, which kills your cdma antenna. Next re-enable wifi and run another test and see if it fixes the issue. I go from 56k speeds to 3mbps standing in the same spot.
While not an ideal way to use your droid I think it proves that it is a phone issue and not a router issue as some suggest.
And regardless of whether the my router is outputting in mixed mode, greenfield, B/G/N, G/N, or N only, the speeds with the X never come close to those on Droid 1.
Does it keep working for any length of time? Every time I reset mine I am good for 2 mins or so.