Just wondering if I'm going to gain much by changing my current powerex Rdms to gorillas for my severne sails.

Masts are "inviduals", so if your current Powerex masts are working well with your sails, don´t update.
I think it´s wise to keep at least one set of your old masts anyway as an emergency replacement one´s.
Sometimes new recommended masts are not suitable for your old sails even if they are from the same brand as your sails.
Mast&Sail combination is the most critical component in your rig, and usually safest way is to purchase new mast/sail package. Building a rig from different manufactures parts takes more knowledge ie. like customizing your own PC from components. The result can be wickedly good or disaster :)

I agree with Finland. Ive had so many problems with mast /sail set ups even from the same brand. some brands even change their mast curves so your new masts are now obsolete and your old ones are quite suitable for another brand. I've almost got two types of mast curves ,stiff top and constant curve in 400 and 430. Every time I sell a spare mast I end up regretting it as the sail brand I like ends up changing the mast curve and the brand I've been forced to go to would have suited my old masts. Drives me nuts.

I've had a 400 rdm powerex mast for a while and found it fine on my severnes up until last years 4.8 which didn't rig very well at all. Same again with this years so I've just rigged it with my 370 gorilla. I've decided now though to trade in my powerex and for a severne. So if anyone wants give me a yell! But really if it's rigging ok I wouldn't worry about it