According to these two links coil uturn Pikes are about 1lb lighter than the 55s that are currently on the bike.
http://www.marzocchi.com/template/detailProdotti.asp?LN=UK&idC=1592&IdFolder=113&idMY=56695&uf=IU&IdOggetto=56811
http://www.bikeradar.com/gear/category/components/forks-suspension/product/review-rockshox-pike-454-u-turn-10-37495
So that in itself is a pretty good weight saving in my eyes, yes you could get lighter forks but I doubt they would suit the character of the bike and they would cost more.
Looking at the specs also shows that the axle to crown height of the Pike is 29mm shorter than the 55. This will steepen things up a bit but also make the bike easier to climb because the front end is lower. With this in mind maybe a 150mm Sektor Dual Position Coil would be a better bet. As this would keep the front end high and still allow you to drop it for the climbs.
As for air v coil it basically goes like this.
Air
Lighter
More tunable for rider weight
More complex
More expensive to maintain and probably buy
Unreliable external travel adjust.
Coil
Simple
Cheaper to buy and maintain
Better external travel adjust especially uturn
Need a new coil if they are too hard/soft for you.
Horses for courses really, I have air on my 160mm FS and coil on my 140mm HT both work great.