Old news, sorry, but last year Boards mag physically measured a whole range of masts to provide us with comparative data. This should make it easier to figure out what "other brand" masts will fit your sail.
A rogue mast? -
Poor sucker who bought that - how would you ever know that the 'perfect ' matching mast you have handed over your hard earned for, dosn't do the job!
Whatever happened to quality control?
Could you imagine going back to the shop with a mast in perfect condition and saying to the staff-
"excuse me sir I have a rougue mast can yo swap it for another!"
Staff reply:-
"WTF"
does it make that much of a difference...
Just say i rigged my NP Combat on a NP X9 with an IMCS stiffness of 20.3, then rigged the combat on a MK RD 100 with 24.8 IMCS stiffness, with being both different types of bend curves.... would it matter when doing bump and jump stuff, and a bit of wave riding?? 
Surely the best way to find out whether a mast is compatible is to rig and sail with that mast?
I've been communicating via Seabreeze forum and email lately with Severne and KA sail designers re mast compatibility with their sails (I use a NP mast at present) and there appears to be many 'grey' areas when it comes to mast compatibility! Ultimately, I would agree with the sail designer if they give an opinion on how well or poorly a mast would work with their sails, however many people (including myself) have used the so-called 'wrong' mast in a sail and it still performs quite well (according to their own standards!).
Example: I used NP X3 and X6 flex-top masts (with bend curve ratings somewhere between 14-17 according to Boards mag) in an 04 4.5 Gaastra Poison which would normally work best with a stiff-top mast (bend curve rating around 10). Whilst the X3 did appear to be too soft for the Poison (and for my NP sails as well!), the X6 appeared to work ok (top end handling may have been limited by mast but bottom end was excellent).
Another thing, does anyone think that the mast manufacturers always produce a consistent product? Apparently, based on what I've been told by people in the know, the masts produced by one of the big manufacturers in Italy have become more flex-top in their bend curve over the past two years.
To quote Boards mag mast test:
With respect to Leech (author of this post), I think that posting scanned images from a magazine article (oops, I did it too!) is somewhat misleading as I believe that the articles need to be read in conjunction with the test results to really get a decent picture of what's happening!
Yes it's true. You should all go and pay for the magazine and read the article. It also contains a wave sail review with reference to masts that work well for each.
Get it here: http://www.zinio.com/gncissue?is=250662045&ns=aus
But I think the stats are Ok on their own for general reference. If your sails just haven't felt right on, say a powerex RDM (flex-top), and the brand-mast of your sail maker is stiff-top, then that could be the problem?
