Something to consider that Dylan Johnson has been mentioning lately, is that he feels the industry is lagging behind in figuring out the wider tires are faster for gravel. He mentioned getting someone to buy and send him 47C Pathfinders from Canada as he couldn’t get them and it was his intention to use them for racing in 2023. He also ended up racing his Factor HT MTB with drop bars, rigid fork and Conti Race Kings (2.2 I think) after testing it back to back with his gravel bike and finding the MTB drop bar build was faster overall for one of the races (maybe Big Sugar?).
I think if I was to buy a new gravel bike I would want something that could accommodate at least a 45c tire, which may help weed out some potentials.
This would disqualify the Aspero and the Kaius but I believe the others you listed can at least handle a 45c. Some others to consider could be the Lauf Seigla Rigid, 3T Exploro Ultra and the Canyon Grizl.
My current bike maxes out at 42c and I’ve never ridden anything but 40c with it and do ride blue level single track with it (fully rigid) but don’t doubt the idea that, to a point bigger may be bigger with may moving to 30c on road now, my winter road build is 32c.
I won’t be shopping for a gravel bike till 2025-26, (new road race bike planned for 2024) but when I do I will be looking for big tire clearance but something that is still suitable for CX (my current gravel bike serves as a winter road machine and races gravel and CX with a couple sets of wheels) I think some of the more exaggerated gravel rigs are getting a bit long and a bit too slack to navigate between the tape effectively or it may come down to needing a separate CX and gravel bike.
Factor Ostro Gravel or Factor LS would be two bikes to consider. I ride a Factor ONE road bike, any I’m good friends with my mechanic who sells the bikes. I’ve gotten the chance to ride both the Ostro Gravel and the LS a few times, and I can barely tell a difference from my road bike to be honest. I also owned a Crux for a while, and although I really liked that bike, I would never choose it over an LS.
I’d definitely add the Factor Ostro Gravel to the list. Especially with the new aero bar they just released and the ease of adding TT extensions to it. And the price isn’t bad. Not sure why you’d be hesitant with Factor, they make really nice bikes and equipment. I ride a Tarmac SL7 now, but if I was buying a new bike the Ostro VAM would be high on the list.
The BMC would be up there on my list as well. Such a beautiful bike. And the tire clearance should suit 95% of riders. There aren’t too many races you’d need any bigger. Not if you’re trying to go fast.
I have a Specialized Crux and it’s a great bike. But, if you just want a gravel racing machine, I think there are better bikes. I use mine mostly for cross, and bought it as a jack of all trades kind of bike. So with that, you get a master of none situation. I’m by no means pushing my bikes to the limit, so it fits me fine. I wanted exposed cables because like I said, it’s mostly a cross bike, and I don’t see the benefit of full integration. But if you want aero, there are the bikes listed above that’ll get you hidden cables. The Crux is super light, which is great when you’re picking the bike up a lot for cross, less needed for long gravel races. With road wheels it’s the same weight as my Tarmac.
Just going from what the brands themselves say spec wise, from Cervelo
"We designed Aspero to fit most 700c x 42mm or 650b x 49mm wheel/tire combinations. Of course, there are variables—rim width, tire casing, and tread depth—which will affect final clearance. We (and the International Organization for Standardization, or ISO), always recommend 4mm of clearance between the tire and frame.
**New Shimano road (not gravel) 12 speed front derailleurs reduce tire clearance in the rear of the frame to 700x38c or 650x45b."
I expect most under estimate the actual tire size they can accommodate as if running wheels with wider inner widths they can over inflate slightly and to allow for some mud clearance, in some cases, like unbound it wouldn’t matter what mud clearance you had but I think in general, to prevent you from wearing out your frame prematurely brands factor in a certain amount of mud clearance when suggesting the max tire size they can handle.