Well, I can help with this one seeing is I have both.
The first thing I will say, the RC6 is a better knife, in every aspect, except the price to some however. That said, I like you had wanted a USMC model for a long time, when I got it I was not disappointed. A tried and true Carbon steel, good sheath, good handle and a decent grind for a production knife.
Lets get a few pics going.
First up the RC6, 1095 carbon steel, Full flat grind with a secondary bevel(which I convex for that extra umph) A "real" full tang, as opposed to the Ka-bar which has a full tang, but it not the full width of the handle, just a RAT tang. the sheath on the RC6 is a higher quality, Micarta handles and a somewhat abrasive coating(more so than the ka-bar)
A great combo with a folding saw.
Good battoner.
Also makes a great ferro striker, just a little loss to shaving ability.
Now for the Ka-bar.
While I dont have the knife now (sent it to a fellow board member) While I had it I loved it. It was a decent cutter (kinda like a BK7) would baton any wood I needed it too, also If you want a knife for fighting, its the one to go with.

It Also sports a 1095 carbon steel blade, Mind had leather stacked handles, and a leather sheath, but I also have a 8" tanto which came with the plastic sheath. It has a Saber grind with a secondary bevel (both knife I believe are at 20* per side) All in all a good field knife for heavier stuff, can cut you camp wood, build a shelter with ease and skin a rabbit should the need arise. (yes I have done it)
I personally bent the top portion of the guard down to choke up some with the thumb, I recommend you do the same.
For reference on size.
Really not the different from a 119 either.
Wow, all this talk is making me want another one, thanks bud now I need to go buy another one.
So, in the end, if you can wait, I would say do so and get the RC6 when you can manage it. On the other side, if your sitting stur crazy wanting a new knife and that ka-bar is calling out to ya, go for its certainly no slouch. Its like comparing a Casio to a Citizen, sure there is a price difference but in the end they do the same thing, they just bring it in a different platform.
Got any more questions post away, or e-mail if the need arises.