I had the savage x flux hp for a long time, ended up with 6S in it. But I had a rc4me.us transmission with a center diff in it. Pretty sure I had 750K in the center to help make it more drivable on 4S, but ended up putting 6S in it and changed to 500K then gearing it down to 16/48. I ran the castle MMX/2200kv 1515 in it and it ran warm (also runs warm in my maxx 4s on 6S... so who knows). I'd suggest a larger motor with more torque and a max6 esc to give you a bit more headroom.
It was still a wheelie happy idiot. I ran trencher 3.8's on it and I wrapped them with 550lb cored kevlar cord. My first run blew both front tires off the wheels within 3 minutes... I then pilfered tires off my outcast (also had trencher MT 3.8's on it, but they were wrapped), then it was fine. I didn't need to wrap them on 4S with 21/44 gearing.
I also ran 4 big bores on it with associated 40wt with yellow long springs on the rear and white long springs on the front. Then it would handle the big jumps pretty good.
My only real warning, DO NOT RUN RPM ARMS WITH 4 SHOCKS! They twist and snap the shock ends off. Took me a while to figure out what was going on and that was before finding rc4me.us as a source for parts, so I was paying $25 to get the parts tree with 4 shock ends on it.
Also, I found that the integy rear axle carriers worked well to get rid of the rear turnbuckles. I ran those on my nitro X and flux hp for a long time without any issues. One of the few integy parts I'd buy again if needed.
I had mine geared/setup to run at a grass bmx track that I run at a lot, so my gearing might be a bit low if your on dirt/pavement more than your on grass.
This was my last run with it... some days, I just could not buy a good landing with any truck... this appeared to be one of those days. The text at the beginning has the wrong spur/pinion in it, but I had already deleted the source files, so I just mentioned it in the description.