Hi Gav.
We hummed and hahed over the 540 or 530 and like cabbie37 we ended up going with the longer beds of the 540. We found it really useful to spend a morning at AL in Poole were we could sit in all the different styles for real.

We started sleeping as two singles but quickly changed it to a large double and sleeping across it makes a massive double. Also like cabbie sometimes we leave the double up for a few days and other times we put the bed away to have the large front lounge. The Troll is really a bit of aTardis. Hope you get one and enjoy.
MikeT