RPM doesn't sell arms for the xxx-nt, or at least they didn't used to. RPM sells arms for both the jato and rc10gt though.
The jato is fun though. The steering is ridiculously sloppy, but it's a pretty tough little rig for a basher. I bash only, so I can't say how good it would be for racing. It takes the same jumps as my aftershock and seems to deal with it pretty unfazed. I have RPM arms all around and an after market pipe/header. The stock pipe sucked and the stock header broke off after a couple hard landings (just like all of traxxas stupid headers do).
I bought/sought out the jato because of the two speed. 7 years ago when I first got into the hobby, my first truck was a xxx-nt. As a basher, that was a horrible truck. I busted a ton of arms and pivot blocks. I'm sure it was a very capable racer... but I didn't race. I also didn't know what I was doing when I bought it.
Now, with some time and experience under my belt, I wanted another 2wd to putts around with, but I didn't like that you had to sacrifice off the line torque or top speed because of the single speed. The jato fits the bill perfectly for me. I have it geared low (wheelies are cool) and it still cooks when it hits second gear. I'm running the original 2.5 jato with an 18T CB. I think it comes stock with 20 or 22. Too tall geared for me and for the grass. Even on pavement it took forever for it to get up to speed with the 2.5. With the lower gearing, it gets up to top speed pretty quickly and is still pretty fast.
Sorry for the rambling...