I loved doing just that in Cod4 just because there was fewer kills to get per gun, so you could go through a prestige nicely by going through the guns.
On MW2 you could go through the guns. I could complete mastery on the M16, FAMAS, SCAR and ACR in one prestige. Thats with all the FMJ kills too. I guess domination games help with that.
Also I liked all the killstreaks on MW2, I tended to be using them to get kilsl rather than being killed by them so I didn't mind them.
Obviously I didn't bother with guns I didnt like.