900g will be an enormous difference. The bike will pedal and accelerate way better, it will hold speed better, suspension will activate better, it will pop and jump way better. But there are a few conditionals.
First of all, how new are your bontrager big earls? If they're newer then 2009, then you probably won't be shaving 900 grams off the wheelset, and you'll be loosing that mostly in tires. If they're older big earls, then pretty much any wheelset you get will be miles of smiles better.
Newer bontrager big earls, for all of their faults, are definitely not tanks. They use 2spoke cross on a 530g rim. The rim already dings like cheese, and I haven't encountered many rims that weight (or lighter) that don't also ding easily. (I'm on my 6th rim within a year - and my builds are all good enough that even when I fold the rim it doesn't go out of true). The hubs are fairly light re-branded dt-swiss hubs, so sealed bearings and star ratchet engagement. You could shave a bit of weight on the wheelset, but chances are, if your wheels are 2009 or newer, you're loosing weight on the tires. You could reasonably loose about 300g on the wheelset and still have a workable race wheelset, but that would be a very light wheelset and a "for race run only" setup.
If you're loosing most of that weight from tires (which it sounds like you are), knowing your tire setup becomes an important variable. Are you considering singleply tires? 2.35? or are you moving from some tank tire to a dual ply minion/highroller combo? If your maxxis tires weigh less then 1100g, chances are you're not running dual ply, and if you're racing beginner, that shouldn't be a probably, but unless you're really really really smooth, anything above sport and you'll probably be getting pinch flats the whole way down.
Hope that helps. Let us know whether you're running pre 2009 big earls and what your tire choices are.