Your fork will be fine for the Spot. DT has beefed up the headtube for people who want to run forks up to 160mm (which he will warranty). How tall are you? I'm 5'11 and got a large, best fitting bike I've owned, I was one of those people that was always between medium and large.
I think Bromley Bikes have some frames at £1495, a few other places too.
All the bikes you've mentioned are great and you won't go wrong with any of them.
Why didn't you try it with the same rebound? Seems like a pointless test to me. It could be that it felt better on the second run due to slower rebound.
I fancy some Alpine action again coogan. We will have to weigh our DW Spots though, just to be sure they work ok. Plus we have to make sure they look good in the car park. (please make sure your Spot is angled so everyone can see it).
You can run longer forks on the DW Spots because the back end doesn't squat down at all. I run mine with a Lyrik and don't really wind the fork down as the front end doesn't wander. I didn't even touch the travel adjust even on longer climbs in the Alps.