Hmm, are you upgrading your current bike or buying a new bike ?? If youre upgrading from 10 speed, the old freehub wont fit since 11speed is abit wider 1.85mm, need to change freehub and redish current wheelset if changing.
105 Di2 wont be out at least for another 2-3 years at least.
I ridden Ultegra 6800 (just the shifters and front D for about 1.3K km since i got my bike in late sept) The biggest draw for me is that the big shifting pedal is made out of carbon fibre. Its quite lame to put carbon fibre there since it saves a few gram, but for me, its much better because the metal paddles will corrode if there is a scratch that penetrates the protective layer.
FWB did some testing and the ultegra was the stiffest of all the cranks tested.
I have not experienced chain drop, or trouble while shifting under load, I do not like the downshift though, since the response is quite muted instead of the loud sound i expect to hear lol.
All the shifting is roughly the same quality, just that ultegra shifts abit smoother.
