The loudness and acoustic in general depends a lot on the shape and materials used in the church building. As is common in the states, our church is wood with a carpeted floor in the loft and nave (unfortunately!). I really have to crank up the volume to get it to the congregation downstairs. And yes, I notice a big difference between an empty and full church. My Priest would often tell me to crank it halfway through the service when we first got it installed and I've never had a complaint that it's too loud (which seems to be unusual from what I hear.) It's electric, but we also have a little 3-rank pipe organ I use for quieter preludes, choir, and communion music.
As an aside, I have to tell you that my wife and I had a wonderful vacation 2 years ago in Scotland to celebrate our 25th wedding anniversary. We didn't get up as far north as you live, but we made it to the Isle of Skye. Sadly, I didn't get a chance to try out any organs while visiting the country. We visited the big church next to the Sterling castle while they were having some sort of open house. They told me it housed the largest organ in Scotland. I had no idea. Probably the highlight from an organ perspective, however, was to visit St. Paul's in Edinburgh on a Sunday morning and hearing the organ and choir play. That was really great.
