Originally Posted by
2WheelWilly
this is a relatively recent 105 groupset--I'd say 2018 or later
What you are looking at might be a version later, but the 105 5800 group that came out circa 2016 that I put on my 1991 Scwhinn Paramount was the best shifting group I ever had. Not that I've had a lot. I was friction shifting till I made that switch. I'd even go so far as to say that it shifted faster and more responsively than my current Ultegra 8000 series Di2. However the 3 plus years maintenance free aspect that I've had with Di2 goes a long way to give it more favor if everything else about a bike is equal. But I do miss the more perfect shifting when the front and rear of my 105 5800 were shifted at the same time.
I was always able to trim out the rub in the big/big combo with the 105. But that Paramount had longer chain stays than my current Tarmac and other bikes I've check the length of.
Between Ultegra and 105, weight is the main difference between the two. Ultegra is quite a bit lighter.