linear encoder protection, stepper motor 'power rating' question, motor temperature

Regarding protecting linear encoders, the RSF-Elektronik 'spar' or linear
encoder I looked at has rubber 'weather strip' sealing out debris. Specs
have friction with and without rubber strips.

My question:

How to decide 'hp rating' for components like shaft couplings and pulleys,
etc. with a large stepper? Running a motor at it's rated current but with
different power supplies gives one different numbers to think about. 5A at
24 V is 70W, but 5A on something like a Compumotor or Superior Electric
drive with 170 or 340 VDC bus...makes me wonder what's being delivered to
that motor!

Contrary to the discussion on this list that higher voltage drive reduces
the current requirement, commercial drives pump in the current they're
jumpered for, and another sobering thought is that some of those big drives
have 3 phase 208 voltage supply, and have big fans and heatsinks. I guess
the electric bill would tell the story, but I have a hard time seeing 90 V @
13.2 A per phase (x2) = 3.19 hp. The motor is smaller than a 3/4 hp
induction or synchronous motor...could the above numbers be 'peak hp', like
vacuum cleaners specify?

Something doesn't add up for me.

Murray