There's always the Trekking bar option also, it'll add about as much reach as a mustache bar and fits MTB controls.



Here's a setup I have on one of my bikes. I had to shave down the barends a bit to get the controls on but makes for a nice riding position, IMO.


Controls on the barends by Lester Of Puppets, on Flickr

I'd ride a bit with the stock bar placing your hands in the flat area to get an idea if a flat bar would give you plenty of reach first, then consider other more "reachy" options.