Thanks Ole, My guiding has been pretty good since giving the mount a tune up & belt mod back in Feb. I am typically seeing an RMS of 0.2-0.3 arc seconds and a peak of around 1.5 arc seconds My image scale is 1.76 Arc seconds / pixel so i am happy that the stars stay on the same pixel for the whole exposure.
I may grab a load of shorter subs tonight if i decide to get more data on M81 & M82, I'm not sure that i'll stop using darks though,
I have a pretty extensive library of dark frames containing 60, 120, 240, 300, 600, 900, 1200, 1500 & 1800 seconds, each of those is split in to different temperatures from 5 degrees C up to 25 degrees C in 5 degree increments and each group has a minimum of 25 individual darks, add to this the Bias frames & Flat Frames for every 45 degree of rotator movement bringing the grand total of all calibration frames up to around 1400, of course these have now been replaced by master files to save time & disk space. So I pretty much have a set of calibration frames for any temperature, exposure or rotator angle I may wish to use.
You're right about imaging without a flattener, I never got around to buying one, and probably wont bother for this OTA, I'll be getting a Officina Stellare RH Veloce 200 MK2 AT some time this year, considering that it will be around the same focal length but MUCH faster at f/3 it will make the APO some what obsolete!