It's not too surprising the soundstage will sound larger, that's a result of the bigger speakers extra bass increasing the depth and scale of the sound and no less than might be expected by increasing your budget by 150%. It comparing the proverbial apples and oranges.
The Arcam is no SPL monster, but it is very nice sounding so, if you have such a flexible budget, have you considered demoing better speakers, rather than just larger?
MA RS1s for instance? For that matter, there's great range of interesting speakers available at that money, from a few names that may be less familiar - Take a look. Just a thought...
I think I'm pretty much sold on floorstanders now. Plus the BR5's are nice and compact. It just seemed the mid range sound was alot warmer, not as harsh - the B&W 685's I tried sounded very harsh. However, maybe I will give the RS1s a listen before i finally commit.