Originally Posted by G-BOAC
I always err on the side of caution. I mean, what's the worst case here...another hour in the Concorde Room sipping champagne?! I've had far worse hours

And more often than not, I find so long as I have my laptop + a 'net connection, I can do everything I would at home/the office work-wise anyway...so getting to the lounges earlier is never any great hardship for me [I guess on a Saturday if you have a family to worry about though, the extra hour may be more valuable to you elsewhere].
Thanks to all for useful input.
I do have family so the hour is valuable, but probably not valuable enough to risk missing the flight and ending up going overnight on Gulf Air. So I think I'll aim for two hours before.
Unfortunately I don't drink alcohol and fly (yes, such people do exist) so all no cahmpagne for me.