I tried both sizes of bar on my C8 while I was changing over mounts, the wider "D" is definitely more rigid. I am not sure how you would mount the bars to a truss dob, wouldn't a ring either side of the current pivot point give the best balance? Then just a short "D" bar would be cheaper. Its going to be interesting to see if the mount takes it. I tried my 200mm dob on a EQ5 with rings and it was a bit wobbly
