Guiding isn't the problem, LP is the problem. SNR goes to hell after about 45 seconds. So much skyglow from CBD. Even a C80A pale blue filter helps to kill some red sky. I may give that another try. Longer exposures with reduced sensitivity but might cut through the red.
The 450D has thermal issues at about 2 mins, the SONY doesn't have heat issues ( lovely camera
) but it's a mission to get critical focus without having a BYE equivalent for it and I'd still need a LP filter or go narrow band to manage longer exposures.
Yoddha (APT) is working on a SONY interface so I've got my fingers crossed it's soon as I'd love to be using it. It also has a customisable White Balance system inside so I can set sensitivity away from the red spectrum end.