Here is my guide log from the other night, as an example of a HEQ5Pro that is at the upper limit. The payload on this is:
8" f6 Newt,
Meade DSI Pro as a guide cam attached to the finder scope,
Canon 1100D DSLR (Thank goodness it's a plastic body, so not as much weight.
).
I don't stress too much about the weight it's carrying. It seems to do OK in the guiding department, although I haven't looked too closely at the numbers. From memory, the total RMS the other night was running around 0.8". I have no idea if that is good or bad.
I was running 2 minute exposures and the stars looked round. I tried a 5 minute exposure to see how far I could push it, but the stars were a little elongated on that one.
cheers,
Andrew