When I left for University in 1978 and sort of gave up cycling, 126mm would fit 5 speed, 6 speed, 7 speed compact freewheels........and the new ish Shimano freehub initially came as a 6 speed.
I have four pairs of wheels fitted with various 7 speed metalwork all set up at 126mm - the hubs are Miche Superfast, Shimano 105 (freehub) and Campagnolo C Record. I think that you only need to go for 130mm when you get to 8 speed and beyond.