RM – how tall are you?
I'm 6'3" and ride a 20" Anthem X. The fit is pretty good for most riding, but I've got a lot of seatpost showing and the cockpit feels a tad short compared to my 21" Airborne HT. Overall though, that's no bad thing. The Airborne geometry is long and low, and that bike is minutes faster on climbs – but the Anthem gains with speed and control everywhere else. The Airborne feels properly scary on the descents now.
Also, I previously tried the XL Anthem (not X), and that was comedy gate riding – horrid.
so overall – I'd be more tempted with smaller more chuckable frame size, longer stem (but try stock stem first) and seat right up.