hi Neil,
I use a 12" newt on my eq8 - it handles the weight with ease.
I think a 14" scope is likely fine and I would guess a 16" is pushing it to the limits. they do have a bit of backlash but are strong.
might be worth looking at the yahoo group
https://groups.yahoo.com/neo/groups/SkywatcherEQ8/info
Cheers
Rusty