11s Ultegra Di2 vs 12s 105 Di2

[jrynb]

I'm looking to buy/build a bike in the coming year, likely sometime this fall, and have been thinking about groupset choice. I'm primarily a racer so my decision would mostly be performance-oriented, but I'm not closed off to other suggestions.

My budget is rather tight (around $2500) so I may, in actuality, be restricted to 11s only. That being said, I'm curious to hear people's thoughts. My personal considerations are:

Ultegra 11s Di2
- lighter by about 328g/0.72lbs
- probably less expensive
- Nicer materials
- I've heard shifting quality may not be on par with 12s 105 Di2
- Do I really need the extra gear?

105 12s Di2
- extra gearing
- supposedly better shifting performance

At the moment I am leaning towards Ultegra but am slightly worried about the ease of finding parts in the coming years, though I really hope that won't be an issue.