I did that on my FX without noticing any real difference. Tried 30 but took most of the fun out of the ride. Put a 28, more fun but still not as much as stock. Have to get around to putting the 25 back on.
Did the same with my SR, put the High speed rear on. Slowed it WAY down, probably would have been better if I had put the 25 on the front. Again, didn't have it on long enough to notice a difference.
Put pressure in tires to maximum listed on the side. That should get you a reasonable increase without additional cost. The Touring screen seems to help as well