Brompton owners

69gi is a lot more tiring on a brompton than it is on a normal bike if you're doing more than a couple of miles.

I have s3 with +8% gearing which gives 69GI in middle gear and i definitely feel it in my legs more than riding my old fixed.

Well there's the rolling resistance of small wheels, but for your average 'intermediate' rider, 69" on a Brompton seems okay for commuting. I had a 2-speed, but converted it to SS, plus switched out the stock 12t for a 13t to drop the gear from 75ish to 69 (with Marathons). It's great about town, and I managed a flattish TNRC on it too, plus a ride out, so it was 65 miles. I had fairly good legs at the time, and got the usual slight lower back ache from 4ish hours in a shorter/more upright position, but I think you'd be good for more than 'a couple of miles'.

When I used it for a hilly Kent TNRC before the absolute-piece-of-shit 2 speed 'mech' died after a pathetic number of miles, I did have to use the 50something" gear for Exedown, but mainly because I didn't want to snap the stem off.