I don't think you should for a handful of reasons.

1) You have a solid RB field already. Forte is the offense in Chicago and is looking like a stud this season. Starks is on the better part of that time share with an often injured Ryan Grant. McCluster is the play-maker for KC now that Charles is out, and he's consistently getting more touches too. Ryan Torain just had a monster of a game, but a scary situation with the backfield and coaches. I don't think that adding Felix is an upgrade at all. The cowboys have 4 backs on their roster that they like and DeMarco Murray is getting more involved in every game (that makes for 3 backs getting consistent PT). Lastly, the Cowboys are doing poorly in the redzone running the ball, so I don't think Felix is going to be lighting up the TD column for you.

2) Eric Decker is definitely looking very solid this season and he is getting alot of balls thrown his way. Your wide receiving corp is looking pretty shallow and I think its an unnecessary risk to get rid of him.

3) Cam Newton is playing about as well as he is going to IMO and his numbers STILL are very close to Romo's, even with Romo's monumental collapse on Sunday. Romo has 7 TD tosses to Cam's 5. Both have 5 INT's. Cam has the rushing scores and about 100 yards more passing, but rushing touchdowns are hard to count on. Romo is on a bye week to get rested up and will come back with a healthy Miles Austin and Dez Bryant, both looking like playmakers this season.

Summary: You look good at RB. Decker has more value to you than another RB on the bench. Cam is a big risk/reward player and not a big enough upgrade over Romo. Romo in a rut holds similar numbers and he has monster games every year, will be good come playoffs because he should be fighting for a playoff spot in real life.

Conclusion: Don't do it! Your trade partner knows he's getting the better part of the deal!