Done it in 3.30, been support crew for a few other years, the weather makes a massive difference to times, as does the ability to ride a cross bike over traditional mountain bike style descents, and the ability to get stuck in on the road, and the ability to get up the hills with your bike on your back.
Spare bike if you can, with knowledgeable support guy, who knows where to be so you can run/roll as fast as you can knowing there will be a new bike or new wheel at a certain point.
Good feeding strategy; camelbak, plus gels, plus other stuff if you require.
Above all, the ability to save your bike, not puncture and keep on keeping on is the most important.
Training strategy; three hour rides, with long bike carries in the middle, get used to riding tired and learn not to make stupid mistakes…