Honestly, for the shelter building and batoning, the RC6 is the best knife for that right now in the RC line.
For MOST bushcraft tasks, like making traps, the finer kinds of work, food prep, etc, the RC3 is the winner.
Even though it's more expensive, I much prefer the RC6 over the SRK or Ka-Bar. The RC6 is the best "do-all" knife in the lineup.
IMO, to get all tasks done, you need a small knife and a big bruiser. The RC3 fits the small knife aspect well (or a SAK or other folder). The big bruiser can be a big knife, like the up coming RC10, a machete, a kukri, a hatchet, etc.
So, if you need a RAT fix, my advise would be to buy an RC3, and wait for either the RC10 or RATchete to come out. Or get an RC6, for the do-all aspect.