S!
Nice pics. I would agree that the exhaust flames are more or less visible mostly at low light conditions, not in broad daylight so clearly, if at all. The DB-engines had direct fuel injection so you really could not adjust the mixture on it. Only adjustable was propellor in case of the automatic failed. Early Bf109's had manual pitch, E-4 and onwards had the automatic with manual as backup(rocker switch on throttle).
Sure the Spitfire or Hurricane is louder as you sit behind the exhaust stacks. In Bf109 they are way lower thus a bit less noise. The Bf110 looks gorgeous, can't wait to fly her! The handling qualities of the Bf109 on the other hand are partially a myth and partially true. If the pilot knows what he is doing it is not any harder to land or take-off in it. Any plane of that era with the big engines were a handful to handle
Have a nice weekend!