A few things chanced when the Capricorn came out. It is not only the larger squaretop mainsails.

The F18 class finally saw the introduction of the wingshape masts (not the same as teardrop shaped masts). And the boats started using daggerboards with alot higher aspect ratio's. This in combination with the improved (custom build) mainsails is causing the gap between your current boat and the F18's to widen.

The rumour has it indeed that 130 kg with the small rig is not entirely competitive, but then again there are alot of rumours about and many of them are simply not true. I do feel however that the smaller jib/spi setup is lacking some serious development. Most crews decide to go with the larger sailplan and carry weight. As far as I know all F18's are designed to optimize the performance with the large sailplans and so by default the small rig is somewhat "forgotten".

Having said all this I don't think the difference is more then 1%-3% around the course at its worst.

Have you considered upgrading your spitfire with a custom build suit of sails. Quite alot can be won here. One-size doesn't fit all. It only narrows the competitive weight range over equalizing racing. Seems a pitty to step of the Spitfire simply because F18's are allowed to develop while the Spitfire remains at it 1999 state of technology. It would appear to me that some 2005 state of the art injection can boost that Spitfire to better competitiveness.

Wouter