Dom_P,
I think drilling the bottom of the cup is less risky than drilling into the acrylic side, but drilling the bottom may be a matter of clearance (the neck and the outside wall of the cup look pretty close) and what type of fitting you use. John Guest makes a really nice 1/4" and 3/8" mini bulkhead that I thought would work.
It's really a toss-up between the Deltec or the H&S...according to the specs, Deltec has a 5" diameter and the H&S 4". All the other dimensions/specs are pretty close. Depending on what your reef's needs are, the Deltec is rated for a larger tank, but don't know if that's worth an additional $125.00!
Luis