Hmmmmm, I'm not sure I can comment on the Maverx masts as I've never seen one before in Australia. Typically, if you put a 460+extendor instead of the 490, you get quite a soft feeling mast. The leach will sit really loose when downhauled and you'll lose a bit of shape in the bottom of the sail. This isn't necessarily a bad thing, and to what extent you can get away with it and not lose too much performance will be how close that mast is to the Severne bend curve.
Just go for it, rig it. May have to put a touch less downhaul on so the leach doesn't collapse completely and see if the cams rotate (all masts are different diameter slightly...urgghh) and weather the sail feels ok. If not, beg/borrow/steal a Severne mast to get in there :-)))
I've been sailing my 7.5m NCX on my 2013 110 and 97. Still waiting for my 2014 boards to arrive later this week! The most fun I have on the 97 when it's powered up +20 knots but certainly can have a blast on the 110 in anything above 12-14 knots and it feels great. The 110 is such a nice board. I'm typically running a powerful 42cm fin with the 7.5m.
GetWindsurfFit.com // The Ultimate Windsurfing Fitness Program.