Agreed, good value for the money and the 'top' Boardmans have always had a good reputation - they always used to be made by Boardman and only the cheaper range of them made in the far east with varying QC issues, but think the real Boardman ones never any problem...
@SoliD will know more as think he has a 9.4?
Thanks for the link too, I'm liking the look of that SLR. Looks like a chunky Tarmac SL8 - not that many of these modern bikes look very different. They would be on my list, as I quite like the idea of getting a 'British' frame as my replacement for the Diverge when the time comes. I'm not that worried about something 'made in england' but really like the idea of supporting a British bike company even if they're making them elsewhere rather than buying a cheap knockoff or something from the US/EU again for my 'everything' bike.
Tough choices but bear in mind the Endurace is likely the faster aero race/road bike than the others, do they still do the Ultimate? That's probably what to look at. The Boardman reads as 'all road' has things like mudguard mounts and good tyre clearances, probably more suited to gravel than the others. The Defy is an endurance road bike, probably has more compliance and clearance while probably being the most comfortable. They're all quite different for various reasons so can't really directly compare them...
Never choose a bike by wheels. They're probably the easiest thing to change & upgrade!
12s 105 Di2 is superb. Maybe marginally more bulky feel - but the RD does so much more on it than older 11s Ultegra di2 where you need junction boxes and wireless units. Better to spend the difference on things like wheels/frames or even cranks.