I have an RD-5500 (9-speed 105) on my Pug, shifting an 11-26 7-speed cassette in friction mode. The B-tension spring is pretty weak on it, so I have a longer M4x0.7 machine screw threaded in about half-way. It won't clear a 28T sprocket, due in most part I think to the weak spring. It was 5 bucks at a co-op, so I run it in this configuration and it works good.
pug_cl_6 by
jnjadcock, on Flickr