Hi Hills, there is a number of differences between international cl5 and promo class 5. Promo's are class 5's but not all class 5's are Promos.
Class 5 for quite a number of years was very big internationally and developments in the class were fast and furious. FISLY often had to interpret or allow/disallow various new ideas that people came up with. However internationally over the last 5-7 years to be competetive on a international racing stage you needed an ever increasing pocket as advancements became more and more costly. Here in Australia we tend to hang on to our yachts for several seasons and can still race locally at a good level. This is not the case elsewhere. Last years yacht design in class 5 was old and slow.
There have been several attempts to regulate class 5 to a more *one design* or cheaper version - both here in Aus and internationally. The Club 88, FEd 5's and Pacific Magics are all examples of this. Aussies started modifying Pacific Magics at about chassis no 7.

One design classes can and do work as Standart as shown.
The Promo class 5 is another attempt to regulate class 5 as a cheaper and simpler land yacht that can be built and raced internationally on a reasonably level playing field rather than just on who has the most money. The big advantage that Promo has over other attempts to regulate class 5 is that it has been ratified by FISLY, none of the others had.
It is currently being raced in Europe (mainly France at the moment), several Sth American countries and here in Aus.
Interestingly enough with the exception of your Pacific Magic mast step your class 5 would be close to fitting into Promo rules.
I like racing class 5, it is fast and fun. However my posket is not deep. Internationally my yachts have not been competetive for some time. However my new Promo is now up there with the best and cost just over $2000 to build.
Promo class still allows quite a latitude for personal design and expression however you need to use a relatively simple chassis, wheel barrow wheels and a dacron sail.
I won't bore you with any further differences between Promo's and Class 5's best way to see the difference is look in the FISLY specs. (Aussie class 5 rules are donkeys years behind the rest of the world)
I'll find some photos of my yacht and post.
cheers
Promo Girl