Thanks everyone for all your input so far.
Seems that I'll need at least f5.6 or less, and 1000mm at absolute minimum, with an ota being whatever the max load my EQ6 will hold, with the QSI WSG8 in place.
That reduces some of the options, affordability being the last one - can't see me spending more than $2k on this, and that will mean parting with my WO FLT 110 first.
Not sure about metal bodied Newts either, as the temperature/focus thing would do my head in,
So that means either a carbon fibre ota or maybe Glen's idea of a Mak Newt which also eliminates the need for coma correctors as Paul mentioned.
More research to do, all good fun hey