I have a few freerace sails with a luft just over 460 (NCX, Turbo and Motos). My 2 mast options are a 430 75% (Severne Gorilla) or a 460 95% (Severne Blu Line).

am I better off with the 95% 460 plus a short extension or 75% 430 with a long extension ?

Or do I need to get a 95% 430 mast ?
am looking to up my speeds but seem to be doing fine with the Gorilla to be honest. Will a big spend buy me more pleasure and speed ? Appreciate any guidance.

what is the recommended mast for your freerace sails?
If they are designed for 460 masts, 430's will be on the soft side (IMCS25 vs 21 for your G2 gorilla). Which isnt necessarily a bad thing depending on your weight and preferences but i suspect you would find the 460 Blu more powerful, stable and responsive
Any chance you can borrow a mates 460 and try?

Whilst all the sails have a little over 460 luff, Severne recommends 430 masts plus long extensions. But would a 460 c95% be stiffer and better than a c75% 430 for pure flatwater speed ?

Tough question ,No 460 will feel stiffer .if you wanted to improve your street racing I would go the blue apex 430 .
at high speeds a more flex mast or high carbon will soak up the bumps and not tend to throw you off .Better return in mast shape
I googled the blue line Severne mast 460 2022-2023 just last week thinking because it had 90 on it ,? was it 90 % ,no some have 70% carbon in some models .so no improvement by going to the blue line 460 .
you need Blue apex has 90 -95 % it has a fibreglass coating .the Apex pro is 100%.. if you can afford a higher carbon mast ,yes .or go RDM . way nicer to use .