The taper and profile of a Scientific Angler GPX fly line is identical for the first 30 feet for the WF and the DT lines. Then the WF rear taper begins at 30 feet and extends back to the shooting line at about 40 feet. So both the DT and WF will roll cast exactly the same for the first 30 feet of line.
See the bottom of pg 4 below:
The WF profile means that you will not get into the shooting line until about 40 feet of fly line our of the rod tip.
So if you are not going to use the long casting capability of the WF beyond say about 40 feet of fly line (then add your leader and rod length), the DT line would be better because it will last twice as long.
If you are going to use that fly line for other types of fishing that will not require much roll casting and you will be shooting line, then get the WF.