Replaced OEM Tekro calipers and much prefer the braking action, feel and looks. Install was straightforward, they do fit Conti GP 4 Season 28's. take your time adjusting them, and you will be rewarded with a firm, responsive feel and great stopping power.
The Ultegra is the 105 caliper with a stiffening frame added, not sure there's much difference, but given the minor costweight delta, the Ultegra seems worth it. And they look good.
When it comes time to replace my chain, I go between Dura-Ace and Ultegra depending on what's available at a good price. I have been extremely happy with both and wear seems to be about the same. Just keep it lubed (about every 300 miles) and wipe it down after every ride.
I purchased this chain as a spare to sit on the shelf for the original on my CX bike. That chain has almost 3000 miles of Nebraska gravel, CX, and MTB singletrack and is in great shape with little wear so far. Like I said, tougher than nails. Paired with the SRAM X-Sync it makes a near bombproof system. Of course, I keep it cleaned and lubed well, but, man, it's a tough chain.
I was able to get a 2019 C-Dale Synapse with the new 105 7000 series build - except for the crank which was an FSA C-Dale design to keep the price under $3K. Im sure it would have been fine but I really like the components to match! As usual, WBW had what I needed. Cannondale would not confirm that the crank would positively fit, but since many of their models come with Ultegra I thought it wouldnt be a problem. My mechanic found the following the stock crank was a press-fit, and FCR7000 is threaded, but the problem was solved with a BB under $50 (cant recall the name but was told this is an excellent parts manufacturer). Looks and rides great, plus no more FrankenBike!