There are many good motors to buy in the 40 to 46 size range.

There have been many, many, many, many, many debates on the virtues and vises of all of them on these forums.

The two motors which seem to stand out the most are:

The OS46FX
The Thunder Tiger 46

Both of these motors have a large following on RCU who swear by them.

Do a search on them and decide for yourself.