I was looking forward to doing the snake this year as a 3, with a decent starting position this go around. I was in the next to last row as a 4 last year and ended up at the bottom of the payout, so it was a good race for me in that regard. However, when registration opened this year, I had about $45 to my name, and decided I liked eating more than the Snake, although it was close.
The Snake is a pretty tough course. It CAN be climbed in the big ring if you take the correct path around the turns and also have the prerequisite room to do so. Like you said, starting position is pretty important. The race can get bogged down on the first couple of laps up the snake, as some people will fall over and others will have to unclip and run up the hill behind them.
I was told that I was down by half a lap when I was going up the snake the third time, with a little more than 2 laps gone. It basically became a time trial after that, catching people going up the snake, trying NOT to pull them around behind me on the downhill and flat section, and repeating every lap. I literally got no help and had no draft the entire race, aside from going downhill behind guys I caught going up the snake, and was then forced to pass on the flat, and let them draft.
The work requirements are pretty unique. Absolutely hammer up the snake, and you should have next to nothing left by the time you hit the top. Recover on the way down, and then get into what should be around your FT/LT or time trial effort or maybe a little lower on the flat section. Repeat 11 more times, in the 4s.
A key to not wasting energy: the insides of the corners on the Snake are VERY steep. Like 25%+. Go through the corners in the middle of the cobbles and save some strain on your legs, albeit going a little further around. See picture with regards to slope.