Living approximately 40min from Gaula river.
I am not expert to say what you should use there but everything depends how much there’s water.
If its 200-400 cubics you might have some troubles with #7 rod.
Under 100cubs and you can easily go with heavier single hand , switch rod or some shorter spey rod.
Last year I was mostly fishing there with single hand #8 rod when the water level was low, didn’t caught any huge ones but 10kg landed and released with single hand pretty quickly.
I was just fishing upper Gaula with single hand when water level was quite normal, no problems there where river is not so wide.
But let’s say :
14-15footer for high water conditions & S4-S6+ sink lines /tips
Low water conditions 11-13ft /single hand #7-9 ,Float, intermediate, S1/S2/S3 heads/tips