Sump tanks are generally the reserve of marine setups, but I don't see any reason you couldn't have a sump. External filters work by draining water from the tank and running it over media before returning it to the tank, which is fully achieveable with a sump as well. A sump will also have the added advantage of being able to hide heaters and other additional equipment inside as well.
The downsides of a sump are that you will need to get your tank drilled, as overflow boxes are unreliable. Obviously you will need space in the cabinet underneath your tank, and you will need to pay out some big bucks to get a tank to fit underneath the tank. This may or may not be expensive, it depends. I'm going marine and was hoping to get a second hand tank to convert to a sump, but the measurements of my stand just didn't match up with the standard sizes tanks come in. If you've got a big cabinet this might not be so much of a problem and you may be able to get hold of a second hand bargain to convert. Hopefully there's a company near you who will cut glass to size, then you just need to get hold of some aquarium safe silicone and put them into place.
As I said, I'm going marine soon and the major advantage of a sump to me is being able to hide the vast amounts of equipment needed. In a freshwater tank, I don't know whether it's worth the effort and expense. For such a big tank it may be that it works out cheaper than two or three large filters, but I wouldn't know.
Perhaps you can share with us why you're thinking of getting a sump?