This is exactly what I did. 2021 CF SL 8 with the regular bar and stem. Swapped the stem for a -17 no spacers underneath. Profile drive aero bars.
The only issue is the 1 1/4 steerer makes stem options really limited. Luckily Ritchey makes some that are very affordable.
I would buy this bike again no questions. It’s plenty fast. Get one with the leafspring seatpost
Same bike! And good point about the steerer - less choice for sure, but at least Giant and a few other smaller brands use the same size, some there were some options. Even Redshift started making a compatible shockstop stem when I was thinking about adding some compliance up front.
Also, I DID notice the newer versions of the CF 8 don’t come with the leaf spring seatpost anymore.
I bought an Endurance and didn’t like much, turns out I sold it and bought a TCR 2021 on Market Place.
Way happier with the TCR. I found the Endurance too relaxed for me. Don’t get me wrong, the bike is nice, it just didn’t fit with my style. BTW, I was coming from a Tarmac, so I guess the TCR is closer, that’s way it fits better.
I’ve thought more about “why not the Aeroad” and I keep coming back to concerns about comfort on long days. Do you have any experience with it?
I do not, but I keep hearing it’s the most comfortable aero bike out there. Plus, if you’re ok with 28mm tires, even more comfort. (I have the Ultimate but originally wanted the Aeroad. I got a great deal on the Ultimate at the time)
I’ve got a 2019 Rim brake Aeroad, and a 2020 disc Endurace, The Aeroad was bought as a snap descision to replace a bike that kept going back to the shop with faults, the Endurace was bought for a road trip where rain was forecast for the entire week (and I panicked)
I’ve done 100 miles on both with no issue, the main differences (been bike fitted on both)
Brakes, but I don’t think thats relevant to you
My desicions were bad as they were always in response to something going wrong (Aeroad because it was summer and I kept lossing my bike to ride to faults), I get a bonus soon as was thinking about selling both and getting one bike to replace both, but really don’t know if I would be throwing good money after bad
Get the one that fits the best, Get the one you like the look of, and put a solid seatpost in a Endurace and everybody will think it’s a Ultimate
I am spoiled, I went through a lot of bikes and currently I have 5. I am writing it not to brag but to say that I have some comparison 
I used to have endurace AL 2015, then endurace CF 2017 I guess. I have Ultimate CF. All rim breaks.
Endurace is shorter with a little bit higher position but still it can be set up agressively (with 0-offset and long stem (110mm) I could adjust the position almost excatly the same as on my Ultimate and Tarmac (both are set up the same following fitting measurements).
Ultimate in terms of handling and overall performance is comparable to Tarmac but it is less comfortable
I think you can’t go wrong with both. Enduace is not a slow bike. Even on the AL version I used to race in the mountains (my target races are about 100km/2000m typically).
To give you some image of my perspective. My favourite bike is Tarmac SL6 rim brake. I have also Giant TCR Advanced 1 Disc and, despite it is realy desent bike, it is worse that Tarmac and Ultimate - for me of course - mainly because of the geometry which I simply don’t like for some reason. Ultimate is comparable to Tarmac but much cheaper. Probably today, choosing between Tarmac and Ultimate I would buy Ultimate mainly because of the price difference.
Having already Gravel or Gravel-ish bike I would buy Ultimate but as only one bike mainly used on the road I would choose Endurace. But once again, and please remember that it is only my perspective, the difference is not that huge you can think.
The best bike I have ever bought regarding the price-value-ride-fun-factor: Endurace AL. The best bike in the terms of price-performance-overall satisfaction: Canyon Ultimate. The best bike I’ve ever used: Tarmac SL6.
The canyon ultimate aero is almost as aero as the aero.
Looking at Tour Int’s numbers, The Ultimate is a really nice riding road bike. The Endurance with the lead spring seat post is an outstanding riding road bike. You can put that post in any round post bike.
As a endurance bike, a current Ultimate would outperform any pre-2015 bike. As an aero bike, it’s be on par with any 2015 bike. Just get the Ultimate if it fits.
I’ve got an Aeroad and have done 140 miles on it in a single ride, no complaints on comfort, not sure if that helps or hinders your choice but just throwing that out there.
Which one did you choose?
Totally agree, I had a Canyon Aeroad with all the spacers under it, got a Enduarace over the Ultimate as i wouldn’t need as many spacers … was racey enough stopped riding the Aeroad
In the words of Chris Miller:
Rather pro the Hubbard bike than Hubbard the pro bike.
I think an endurance bike with a longer, slammed stem looks way better than a race bike with 4cm of spacers and a short stem, or even worse, a positive angle stem. And it likely rides much better.
This is exactly the reason I bought a Giant Defy. To minimize the amount of spacers
I am pretty sure that my brain knowing that my bike looks cool makes the bike faster then any aero gains 