With a 2" diagonal attached the balance point is altered, so you just need to move the scope upwards through the clamp a bit further. The side-effect of this is that you will get more swing room for the diagonal. There are also shorter physical (and therefore focal length) solutions from Baader and Televue. Also more generic SCT diagonals can be found that attach directly to the rear thread also, so they don't have to be all that longer.
IMO the 2" diagonals are worth it, if you are interested in the widest FOV from your scope. Whether it's worth the investment, given that you have the reducer already...it's hard to say, and in an ideal world we'd like to do a back to back comparison
FWIW, I'd remove the reducer when increasing the magnification, for example when viewing planets, as the Pentax eyepieces are really quite sharp...