40's have an effective reach of only about 2'. At 3' it moves the water, but it's really weak. If you have them on the ends of the tank like most folks (i.e. facing each other), they might even have a damping effect on each other. They are not ideal for a long tank. In any event, mp60's are not the cure....a different style of pump is, IMO.
To that end, a Tunze Stream is designed to move water better and has around a 6' reach. To boot: At $285/ea it's more economical as well. A pump on either end, run alternately as a tide simulation, or using whatever flow pattern you want to set up would rock a 180. I've converted more than one 180g tank this way. Be prepared to freak out when you see how much detritus get lifted out of the rocks and sand as soon as the 6105's take effect. A pair for $570 seems like a bargain.
There are a number of other pumps that would be more suitable than the 40's, even multiple other options from Tunze other than the setup I proposed above. But of course there are other makes too.
If you're die-hard on the Vortech's, you'll have to run four of them across the back, possibly making allowances in how your live rock is stacked because they can't be aimed/can't have any obstacles directly in front of them. At around $1500, it's not an economical solution at all, but you will get great flow this way. You can find a few excellent examples of tanks set up this way here on R2R.
And very possible to knock off the glass by accident - not something that's really possible with any other pump.
