I am similar to you in terms of bikes, I have a Vitus Energie Evo CR as my main CX race bike, I also have a Vitus Substance CRS gravel bike that I’ve C’xyfied by changing the wheels, tyres to match the main race bike and gone single ring 40t and 11/36t out back, and made the set-up the same as my race bike – this involved pretty much slamming the stem and dropping it to 80mm to get the shifters in the same position on each bike – and you know what, yes it does feel different, the head tube is massive and the fork legs are deeper on the CRS, but there’s no discernible difference in lap times during races.
See which one has the most scope to play with set-up wrt bar position etc as you don’t really want a sit up and beg / relaxed position, and make sure it has a near horizontal top tube so you can shoulder the bike, sloping top tubes are sodding useless for this as you can’t get your arm through quick enough, if at all.