Hi Mick, I've been wondering the exact same thing lately (I have an F/10 SCT and often wonder whether imaging would be any faster with a Newt).
As a follow-up question to Mick's (however I don't wish to hijack the thread) - is there a standard rule (or ratio) as to how much faster an F/6 is compared to say an F/4? (e.g. is it twice as fast?), and say for F/10 to F/5 will it be 5 times as fast? Or is it a bit more involved than that? I'm guessing it is - I liked Colin's example where you outlined how a camera chip needs to be considered
I'll be following this thread with interest
Cheers, Evan