Pro's:
1. Bigger tank=larger volume of water (dillution of solution is good)
2. If you do it right, the 'deeper' tanks can be fun as they allow for lower light corals.....BUT....people tend to try lower light corals in these situations that really should't be kept in a reef tank because they realy so heavily on filter feeding, and getting them enough food is almost impossible (long term) without causing water quality problems (in absence of some SERIOUS refugium feeding). So, while it's a positive, long term this can be hard to maintain.
3. Deep tanks LOOK GREAT!
Con's:
1. If this tank is glass and not acrylic (which is likely given the dimensions), you are talking about a tank which will likely weigh in excess of 600 pounds EMPTY! 48" high glass will be in excess of 1/2 inch, and weigh a LOT! My 300 gallon tanks took 8 people to really maneuver them around safely, and were placed on concrete floors.
2. Length is better for most fish that you would choose for a tank this size eventually (tangs, etc).
3. Deep tanks suck us into purchased of corals like sun polyps, carnations, tubestreas, etc. which are very unlikely to do well long-term. They also are clam-challenging (though you can engineer clam 'pots' if you plan carefully.
4. A Mag Float will likely not help out much except for keeping micro-algaes off the glass (film algae). Coralines will still require scraping, and this is MUCH more difficult in deeper tanks. I have a heck of a time keeping the front of my 250 clean. I use a Magnavore because the Mag Float has literally no effect through the thickness of my glass (acrylic actually on that tank). My algae magnet runs almost $100 bucks and still won't phase the coralines. Long handled pro-scraper is a pain in the tush! Sigh....
5. Aqua-scaping has to be nearly permanent or you have tumbles that can be catastrophic! Like as in smashed corals or even broken tank! OUCH!
Deep tanks can be amazing! Just be sure you are very serious about it, have lots of time to keep it up, and are more patient and careful in your initial rock placement (acrylic rods in the rock, ties or lots of epoxy).
Best of luck and God bless...