I certainly wouldn't expect a lot of difference.
Going down 2 teeth from the standard 38 rear is just 2/38 = 5.2%
Just about the same as going up 1 tooth from 18 to 19 in front 1/18 = 5.5%
I've spent the last several years defending my choice to retain the standard 18 tooth front sprocket on my C5. I liked the acceleration and low end pickup and didn't really feel I needed longer gearing since I almost never take the bike on the highway.
Eventually, I actually looked under the side cover, counted the teeth on my front sprocket, and found 20 of them. Oops! I have the standard rear sprocket, with 38.