Now you've done it, this is a hobby that can take up most of your disposable income and free time [smash]
Opinions will vary greatly here, but I say it's up to you whether to keep everything Colt or mix and match, this goes beyond the stock to include everything else.  
You should find a Colt stock and try it, then get the new ribbed unit and give that a spin before buying either.  I've had the fiber glass, aluminum and the new model, I like the new one much better, it's a little longer, has a larger and slightly angled butt end and a sling loop where the fix stock's loop is, wheras the original telescopic stock has a slot like longitudinal "loop" at the rear top, it's probably an afterthought.  Unlike the aluminum stock, it won't rattle.  But if you want to put a rubber butt pad or cheek rest, they don't make any for the new model yet.
Bushmaster sells both the new ribbed 4 posiiton model, and the imporved 6 position "original style". [url]bushmaster.com/shopping/buttstocks/[/url]

I like bushmaster and its service, but I like to give my business to smaller shops, as a small business owner/operator I want to support others like me, it takes a lot of sleepless nights, facing many uncertainties, and guts to start your own.  Many business start with the best of intentions but still don't make it, sometimes they just can't compete with the big boys on the block.  I've heard nothing but great things about gunsmoke, I'm going to buy my stuff from them from now on.