Yeah I'm pretty much set on going with 3s. I've had real good succes with 3s in a truggy in the past.
Also why wouldn't you solder to the board? I've been certified in JSTD-001 soldering so if it's a technical issue I don't think I would have a problem there.
Hey I just got done setting my 8ight-B up with a MM and I used a Castle Neu 2650kv. I used 4s and was doing laps around a little bash track and it was pretty fast for the small track. I then used a 3s and it was still a decent speed for the small track.
I'd say if your track isnt that large 3s will run just fine for 30-35 mph. I had it geared for 33mph on 3s and 44mph on 4s. The 2650kv castle motor only got up to 112* F but the MM was a Toasty 160* F. Gearing was 14/48.
I plan on adding a cap and MAYBE a fan, but it was really hot outside and I think the cap may suffice...
Maxx - FLM, MMM, CD Med.36x706s
Raja - FLM Ext. MM, 1512, 4s
SC8ight - MMM, 1520, 6s
D8T - MMM 1717 6s