RE: Turnigy C42-60
My experience with the regular "golden" series is better than with the SK series. I have (had) 5 smaller ones and 2 larger ones. The larger ones I have replaced with Hacker, sorry I don't trust the magnets even after putting CA glue.
On the smaller ones no problems with magnets but shaft is relatively soft. The bearings are not of the highest quality either and if the prop is not absolutely perfectly balanced u will have problems with them.
On the other side 4250-700 and 4240-1050 are performing very good in Element 30 and Acromaster.
Just don't push it to the max power suggested by HK, up to 70% is fine.
Where do you plan to use this motor, may be I can help you choosing a better one?