Originally Posted by Wilfred Laurier

veganbikes 's advice is correct. Switching wheel sizes will not gain you anything but incompatibility hassles.

I disagree with the above advice to get ultra-narrow tires - wider tires, all other things being equal, have less rolling resistance, and also require less pressure, which gives a more comfortable ride and more traction. There are lots of good 26" tires in medium widts (1.5" or so). My favourite is the panaracer Pasela, which rolls like a racing tire, but for a low price.

Bikeman Panaracer Pasela ProTite Tire - 26 x 1.5, Clincher, Wire, Black/Tan, 60tpi

Also, you should know that moving your brake pads to match the braking surface when changing rim sizes will result in a significant change to brake performance. Generally speaking, if you are moving the pads away from the brake's pivot point - as you would have to do if going to a larger wheel size on your bike - you will have less braking power for the same force input at the lever. IF moving from 26" wheels to 650b (27.5), the 12.5mm pad movement required is a significant change over the original distance from the pivot to the pad, and will cut braking power greatly. It might be possible to use non-V-brake compatible levers, which pull less cable but with more tension, with the V brake model linked above. I wouldn't think it would work very well with V-brake 'long pull' levers.