Most routes will gain small to moderate amounts of time. Some will lose. It depends ENTIRELY on how your route is laid out, so it is tough to generalize.
My route is rather sparse (roughly 100 miles, 300 boxes) and I'm going to gain about 8 minutes a day on drive time. I used a wrist watch GPS to measure my route and then wrote a program to figure up the drive time:
RRECS: Drive Time Revisited
Unfortunately, this is still well short of the time it actually takes to drive my route. Most of the roads are "gravel" but are more accurately described as "mud with a few rocks." Seldom do I crack 35mph.
Likewise this new system doesn't consider weather conditions. So if you have to putt along in snow/ice country, no help there either.
If you are driving more then 5190 ft b/n events, they expect you to AVERAGE 39.45mph. Which means you need to cruise at something closer to 45mph to make that average speed (ie if you want the average to be 39.45 mph you have to reach a speed FASTER than that to make up for the time accelerating). So just remember the speeds in the drive time matrix are AVERAGE speeds, you have to reach a peak speed faster than that.
Josh and I are talking about drive time on the next podcast episode. So if you prefer to consume your RRECS info that way, stay tuned!