One more observation:
I already knew this to be the case, but definitely didn't realize the extent. The stock BMW speedo is optimistic. We all know that. What I didn't realize though is just HOW optimistic. Since hooking up the trailtech and having a working tach and speedo, I'm now turning 4180 RPM at 60mph whereas that engine speed had me over 70 mph previously. GPS agreed with my speedo REALLY well too. The stock wheel size setting on the trailtech had me within 1 mph of the GPS at 70mph. No wonder it always took me so long to go everywhere before. I was actually going 60 when I thought I was going 70.