whoooott lipo

[Patrick]

Do all the batteries get that hot or was it just the hecell ones? I'd be suprised if you got the neu and flightpower packs that hot without the motor and esc getting hot as well.
I prefer 5 and 6s over 4s, but 4s is still good, and since your esc and motor seemed to handle it ok it sounds to me that the batteries just weren't up to it. If the other batteries get too hot as well, then you might need to change things.
You are running a motor with a bit higher kv than normal, but people have used them before without issues, so I don't think that by itself would be the problem, because your only geared for ~40 mph. Are you driving it fairly hard?