I knew they were there (I'd moved over so they could pull out of a side road) and I'd been watching the speedo' making sure I was sitting on 70. They told me I was doing 80 on the dual carraigeway

It would be good to have an idea of engine revs in 5th for 40, 50, 60 & 70mph for an atmo with standard wheels. Can anyone help?
The two guys who stopped me were really top blokes and understanding that it's an old car and said they knew I knew they were there. Even had a quick chat about the car before telling me to be careful as if they'd been traffic police they'd have been less lenient. Phew! Unblemished record and first time I've been stopped in 26 years of driving.