I'm sorry Geocycle I've only just noticed your reply.
Regarding the differences regarding my RST and Audax 853, my RST is kitted out for commuting. It is flat barred, has a Son Dynamo hub on Rigida Grizzly CSS rims, lights and a Thorn Expedition Rear Rack. It is also currently shod with Schwalbe Marathon Plus tyres. The Audax has a Carradice Barley on a Sport Rack and medium weight Mavic rims (319) I think.
At a guess I would think that the RST would be about 3 kilos heavier than the Audax, the drop bars on the Audax also put you in a slightly more aerodynamic riding position too. I reckon on a 50 mile ride I would be around 2-3 mph faster.
One bike isn't better any than the other, they are just better at doing specific things. Maybe a Mercury would be the ideal compromise between the two.
Regards,
Neil