If one of your high priorities is gas mileage, that might rule out the DRZ400S. The five-speed vs. six-speed issue is possibly not quite as big an advantage for the 225 as some people think. What Yamaha has done with the new 250 is spread the gears out farther, so there is more of a gap between each gear. The 250 isn't quite as wide from low to high as the 225, but it's close. How they do on the highway depends on vibration as well as gearing.
The closest thing to a direct comparison I've seen is from Duckspanker. You might want to PM him for more information:
Originally Posted by DUCKSPANKER
I have a 08 XT250 and a 05 XT225 I have had some time comparing the two bikes and found them to perform very close, on the street the XT250 is a nicer ride it feels safer in the turns and the front end does feel to light at higher speeds like the XT225 will. On the trail they perform side by side even with the XT250 only having a 5 speed tranny both bikes would take on what ever trail or hill test I performed. Between to two I like the feel of the 08 XT250 a bit more than the XT225.
MPG are so close between the two that I cant give a fair answer yet until I do a 200 mile plus ride with both bikes at the same time this spring, I will have my Bro ride the XT225 and we will test that out. One note the 08 XT250 Tank holds 2.6 and the XT225 only holds 2.3 gals.
So far I am happy with 08 XT250 and will post further evaluations when I get more time to ride.
One more thing, I had a hard time finding Accessories for the 08 XT250 but just found the Bash plate and Cargo Racks from www.turbocity.com
As far as gear ratios go, here's the comparison, widest to narrowest, of some bikes in this class. Note that the 5-speed Yamahas have wider gear spacing than the six-speed KLR or KLX 250s:
3.90 Yamaha XT225 (6 speed) 19.69
3.78 Honda CRF230L (6 speed) 19.12
3.63 Kawasaki Sherpa 250 (6 speed) 18.30
3.46 Yamaha XT250 2008 (5 speed) 17.50
3.45 Yamaha TW200 (5 speed) 17.43
3.36 Yamaha WR250R/WR250X (6 speed) 16.99
3.32 Kawasaki KLR250 (6 speed) 16.76
3.15 Kawasaki KLX250 (6 speed) 15.91
If you care about what the numbers mean you can read it in the opening post in the five-speed vs. six-speed thread: http://www.advrider.com/forums/showthread.php?t=281742
Here are some threads:
fuel mileage 225 vs. 250 http://www.advrider.com/forums/showthread.php?t=319350
on the 250 http://www.advrider.com/forums/showthread.php?t=290853
Other ADVriders you might want to PM for information are justacommuter and The Cameraman.