26" at the smallest. The whole concept behind smaller wheels is to enable you to navigate through rough terrain easier, there's no need for this in what i would assume your commute would be hence why i would recommend sticking to 700. 90% of the specific hybrid bikes out there are 700c, but what we have been selling alot of lately are mountain bikes which the customer has then adapted to become more of a hybrid (slick tyers, bar ends ect..). Also personally speaking i think disk brakes are a bit too powerful for hybrid bikes, sure there good when your tearing down a hill at 40mph and your tyers and rims are getting caped in mud which would pretty much make any sort of rim brake useless, but for stopping at a set of traffic lights the kind of brakes you have on there at the moment are about right. Another problem you may also come accross is finding some 26" rims/tyers narrow enough to sit inside your existing frame and fork set-up. The only 'decent' hybrid i know of that is 26" is the Carrera Subway, which also comes with disk brakes, sounds alot like the one you mentioned in your post. This one by any chance? Obviously all the info i'm giving you, is just information, and if you feel more comfortable then by all means go for a smaller wheel, but honestly, i don't see anything much wrong with the bike as it is currently...