Go easy on the lower rear gears!
You don't want extremely low rpm on the QE2 unless you're keeping up to traffic at 150kph.
I'd put a 700r4 in first with your stock gearing and then decide if you want to change gears.
Here's a link to a speed/rpm calculator. Help you figure it out.
http://www.advanced-ev.com/Calculators/TireSize/