You can use pretty much anything over a 29 gallon tank as they are shallow (PC, T-5, VHO, MH) but if I was interested in keeping stuff in there that needs strong lighting, personally I would go with a 150 watt DE halide pendent.
The 400 watt high bay fixture listed above is not appropriate for a reef setup IMO and a 400 watter would be way overkill even if it was. On that tank I'd go no more than a 250 watt DE.
If you're thinking of the future (the 75 gallon tank you mentioned), 2 X 150 watt DE is nice on a mixed 75 gallon reef tank (assuming standard dimenions, 48" long). 2 X 250 watt mogul or DE is nice if you're looking to keep SPS, clams, anemones, etc. Something to keep in mind if you're planning to expand to the 75 gallon in the future...
JMO...