In reply to caroleb:
i'd echo the replies of anyone here telling you that 25l is a good mm pack size.
i've used a la rush 25l a good few times and i'd highly rate it. (the missus has a rush 27 and rates it also)
no experience of any of the packs you list (since my rush pack hasn't worn out yet), but all i'd say is look at each funtion of the pack. if you really don't think it helps you be efficient in a race get the scissors and cut it off!
it should be a basic bag on your back with not too many pockets. most things stay in it until the evening camp.
the exceptions are hip belt zip pockets - good for necking gels without stopping and ches.t strap bottle pockets if that is how you take you take your drink. obviously this is less important if you are somewhere you can forget bottles and just dip a cup in streams.
balloon beds help you fit everything in a 25l bag and give a good nights kip. anything else is too bulky imo.