As it happens, Glasgow angling are selling Skagits off for £30. I think I'll have the 660 gram for the 15' GT4 Catapult!
I just used the Skagit as an example of the kind of changes in taper that you need to get before a line starts being radically different in a given set of conditions.
A Skagit might be a good idea and I know a few folk who use them when conditions are difficult.
However, they were designed to shift big chunks of tungsten tip and they can be a very blunt instrument.
The best advice I can give is to get out and have a go with what you’ve got. Even better, get a lesson or two before you spend any cash on kit.