Torque, (T), in short, is rotational energy.

------------HP X 5252
T(ft-lbs)=-------------
---------------RPM

Rearranging the above equation yields:

------T X RPM
HP= ----------
--------5252

HP is dependent upon Torque and RPM. One engine may have slightly higher RPM figures than another while it's torque is a little less. Yet both engines can have the same HP.

Torque figures would be a much better way of evaluating an engine.
Servo manufacturers use Torque figures-why don't engine manufacturers???

I agree with Rcflier_gi except for #s 3 and 4. For me they go hand in hand.

The BHP/RPM figures engine manufacturers state are generally not very useful though they do give you an idea of what to expect from an engine.

Once you pick an engine for an application ask around before you buy it.

Hope this helps,
Jeff