Many thx chaps... Most enlightening
BTW I used to go to a sailing club near Pershore when I was a kid.
So 1/10 wave is not necessarily going to help me for astrophotography. Squaring the camera is more important. I happen to have an orion optics OC1 (I think) 2 inch focuser which I'm going to fix onto the tube. I will be using a full frame canon 5d mark ii with a 0.9 x skywatcher coma corrector for imaging.
Having digested the above advice I think will use the brighter, newer, faster, synta f5 mirror AND controversially I will cut the end off the tube in order to reach focus. I mean how hard can it be 😉 (famous last words).
[Maybe I should see if someone is keen to buy it before getting the saw out. Does seem a shame to carve up such a well made scope.]
Also still curious to know whether high quality mirrors make any noticeable difference in DSO astrophotograhy or whether the only real benefit is planetary.