I have experience with both. I bought both bikes in size M and took them to my fitter to figure out which would work better. I kept the SLX.
Th big difference for me was the SLX (stock, without swapping stems and removing the spacer/cutting stem of the CF) is indeed longer and lower. I have orangutan length arms and decent flexibility, so the SLX was a better fit lengthwise and was lower/more aero. I understand you can cut the stem of the CF but then the bento box is in the wind (or you can try to get a smaller one which would be less useful and good luck getting small parts from Canyon… that’s my one major gripe about the company but I digress).
The other major difference for me was pad width. It’s much wider on the CF. That was a plus for the CF for me. I’ve had a lot of difficulty getting the pads on the SLX wide enough for me and have resorted to a somewhat jerry-rigged system of Canyon switch plates and angle brackets to widen the pads which somewhat interferes with the bullhorn grips which is kind of annoying and I may switch to a wider base bar (which wasn’t stocked last time I called Canyon, getting the theme?) (Yes, narow is aero, but comfortable is even faster).
Ultimately, the CF probably would have been easier to dial-in fit because you can use 3rd party parts which are more widely available. The propriety SLX front end is very adjustable and with the right accessories you could probably adjust it however you want (it’s just US Canyon availability of those accessories is spotty).
In terms of adjusting / working on the SLX, I think complaints about working on integrated bike are WAY overblown. If you’ve changed brake pads on a car, changing brake pads on even the most poorly designed super bike is a cinch in comparison. Maybe it takes an extra 10 minutes to remove a couple covers or something and you might have to read the manual the first time you do something, but it doesn’t require an engineering degree as some will have you believe.
I took both for a short test ride and couldn’t tell any difference in frame stiffness, etc. The lower base bars of the SLX made the handling feel much more racey. It’s like the difference between a base 911 and a GT3, both are low and fast, but one feels materially lower/faster. The CF could probably be ridden around on the base bars for a recovery ride. The SLX, not so much, anytime I’m on that bike, I’m going all in.
So net net, I stuck with the SLX and am happy I did. The cable routing is neater. (If you go DI2 on the CF, you have this little rats nest of cables in the bento box which worried me, getting GU gel and going in and out of that all the time). And the bottom line for me is this, I want to get every ounce of speed out of my body as I can. Even though I’m a MOP-ish cyclist, I want to know that on any given day my time is as good as it couple possibly be. I also know myself and any time I compromise to save a few bucks I end up upgrading later anyway for a huge loss in the trade. I’ve never regretting spending more. Some more value-driven people are the opposite and always feel guilty about spending more. So you have to take your own psychology into account. For me personally, I just wanted the “better†bike which the SLX undoubtedly is. Even if you’re value driven, perhaps you could convince yourself since Canyons are 20% or so cheaper than a comparably equipped Cervélo/BMC/etc. the SLX upgrade is “free†by cutting out the middle man.
I’m not a fitter but I think both bikes would probably work for most people. The SLX might require some extra hoops to jump thorough but once you’re through the gauntlet (as I ALMOST am after months of tinkering and waiting on Canyon to get me parts) I think it’s worth it. The CF is probably slightly lower headache especially if the stock configuration could work well for you. If you’ll be switching to an aria stem setup, I’m not sure. You might want to look into how hard it is and how much it will cost you.
Canyon would probably argue otherwise, but given their great return policy, you might as well just order both bike, take both to your fitter like I did and decide for yourself.
Hope that helps…