Unless you have a custom stand that is very long, your standard 220 gallon stand will not accomodate a 72" long tank, not to mention there will be very little room to put stuff under the stand. You may also want to decide how heavy you want to stock the tank and how often you are going to be feeding. I like to have a skimmer rated for 2X the volume of the tank and sump, this allows me some wiggle room in terms of bioload and feeding. If you plan to have a lot of fish then you may want to upgrade to the 250, but if you are going to have less fish and feeding more sparingly then the 200 would be a good choice. The 200 has an 8" diameter reaction chamber, which is what most skimmers have that are rated for 300 gallons or so. That may need to be taken into account when planning a skimmer for a tank that will have a combined water volume of between 300 and 350 gallons.