You want somewhere between 4 to 6 turn overs an hour. (Some people have higher some lower but 4 to 6 seems around normal)
So tanks 40 gals plus estimated sump gals.....x6..... should get you pretty close to what you need
Now there is head pressure loss....meaning the pump has to work really hard to push water straight up and over into the top tank(assuming your going with a basic set up here) Further away its got to go, the more loss of pressure. I found this calculator helpful figuring that out http://www.reefcentral.com/index.php/head-loss-calculator
hmmm
well tank is 40gal the sump is what 15 gallons and the stand is 32in tall then plus tank height... lets call it 48in to pump water up to return line...
so adding tank gallons and sump I'll call it 60gals... so 60x6 equals...360 gph sound right
will look to see how many gallons the eshops sumps hold for both 100 and 200 models.
6x isn't far off, so no big deal, but I like 2x - 4x better as a recommendation. Less likely to cause problems than higher flow rates (which made more sense before propeller pumps came out), yet completely adequate to keep skimmers and such fed. Maybe consider 5x if you think your plumbing is going to clog faster than average, but beyond that is kind of a waste in most cases.
And please remember that we are talking about actual flow rates, not pump ratings or drain rating.
Calculate the amount of head loss your plumbing is going to generate and use the manufactures flow curve to pick the correct pump. Easy! :)
2 schools of thought on this; high turn over and low. I'm a low/lower turnover person myself. I don't even know what my rate is since re-plumbing my tank to a remote sump on the other side of the wall and I'm using an Eheim 1262 for my 80 gal display. My method is to have lower flow so that detritus falls out in the sump. I use my vortechs to move water and keep detritus from settling in the display until it moves over the over flow. This lets me remove a fair amount of detritus when I do water changes.