Hi LEM:
it's pilot judgement,as Boeing likes to say so often.
The bleed trip off NNC says avoid icing conditions. (indeed you arer right in assuming that in this case you can be at cruise alt,low chance of encoutering ice and also a high demand on the pack.)
But at the end of this particular NNC ,it says:
CAUTION : use of wing anti-ice above aprox FL350 may cause bleed trip off and possible loss of cabin pressure.
So you have your answer.You can use wing anti-ice at lower level,as your judgement dictates.(at lower levels...)
Otherwise it would've said : caution: use of wing anti-ice may cause bleed trip off.....(no level specified)
Brgds....
Alex