Zero loss on Force is the front only. Basically Justin nailed it. Zero loss in the rear is pretty cool. Weight difference between component sets is .4lbs.

I had Force and now ride Red. I wouldn't have a problem riding Force with Red shifters.

There is a guy that sells Sram groups on CL in the SF bay area. He will mix and match for you and his prices are really good.

Here is one of his ads. Email him and let him know what you want. I'm guessing a Force group with Red shifters would be about $1000-1100.

http://sfbay.craigslist.org/pen/bik/2832851257.html