Worth 4K more?
Depends on how long you are going to own the car.
After driving my 2010 Challenger with 3.91 gears and a 6-speed 12hrs I think it's worth pulling my Hemi 4-speed from the RR and doing the T56 Magnum swap.
In terms of "what is OD worth" calculated fuel savings is one measure. Payback is pretty long by this measure only. I get it.
How about other measures? Noise, range on a tank of fuel, engine life? This is where OD shines for me. Decent range, moderate noise and I don't wear out my (moderately expensive) engine on a road trip faster than needed. I ran mine from IL to CA and back covering >700 miles/day without un-necessary fatigue, range issues or wear.
For the TKO buzz, the shifter can be one source. The other is the little cap on the shift lever. This alone can buzz. Remove, clean and re-install with a few careful daubs of clear RTV to fix the "cap buzz".
