How quiet are these cabs compared to the cabs on the 6020 or 6030 series? The only info that I can find from Nebraska Tractor Tests is for a 5093E which has a sound level of 78.9 dB as opposed to the 71dB of the 6220. Since 3dB is a 50% increase in sound level, 6dB would be a 100% increase. it...