> Camalots have a larger range, thumb loop but don't have the expendable sling and have a different caming angle (a little less holding power).
I think you meant 'extendable'?
Personally, I rate the Camalots more than the Dragons, owning Camalots but having used a partner's Dragons. I find the extendable sling on the Dragons only marginally more useful than a fixed length sling on the lead, and feel the advantage gained does not outweigh the loss of the thumb loop. Furthermore, I find shortening the sling back to its doubled length when seconding, in order to rack the cam, quite awkward, particularly one-handed on steep ground.
If you can get Camalots for 43 quid, as one poster suggested, I'd go for them. I think that they would make a good complement to the Dragons you already have, particularly as they offer a similar expansion range to the 1,2 and 3 Dragons you are considering.
Of course, this is all just one punter's opinion...