I’ve ridden the Mega twice. In 2007 i was just outside the top 100 which i was chuufed with.
I was riding my DH bike which wasn’t ideal really. As long as you’re a reasonable rider you should be able to keep up with the pace on the downhills. You seem to end up with people of your speed anyway. Where i got nailed was the uphill/flat sections. I was probably top 40 after the snow but lost all my positions to fit guys on XC bikes on the ups. Partly due to a heavy bike, partly due to poor fitness (but i’m no porker).
Practise your snow technique a lot, you can make a lot of places up here and it sets your position for the first twenty minutes. Also, if you fall on the snow, you’re knackered. My mate fell, dropped hjis bike then took five minutes clawing his way back up the hill to his bike.
As far as a bike goes; rock hard tyres, 60psi in qualifying to reduce pinch flats (note however that pressures vary a lot at the top of the hill compared to the bottom), adjustable seatpost, single ring up front with a comedy 12T-34T cassette.
And finally, get a boxxers hand strengthening thingy. Squeeze this everyday for six months and you might be able to hang onto the bars most of the way.