Another question........Motor

With the ice storm up here in NH, I have been in my workshop playing heli hover and trying not to clip the workbenches, lol

Now I run a pack or two 3cell lipo and then I let my motor cool off (400 brushed).

I use an infra red temp probe to check motor temps and even with the heat sink on it , it runs around 148°-154°.

My question is.....whats too hot? I know the range for nitro but not for electric.

Would a brushless run cooler?

Should I just not worry about it? I have fried motors in Evaders (electric car) and E planes before but they had a lot of hours on them.