mudgaurds advice

I'm running the 45s on the winter bike with 32c tyres.  It seems to be the best 'do it all' size.  Might be borderline with 42s but I tend to think the 55s look and feel more like an MTB guard than for a road bike.

yeah that was my concern the 55 will be quite big gaurds to be honest and obviously more than adequate for the tire size but may look out of place. I guess with the 45 its gonna be tight and only just cover the wheel.

45s might indeed be borderline on 700x42 tyres, but it depends how the tyres size up.

This is 700x38 tyres - but a rather plump 38 - with SKS Edge Al46s, and they're only just covered. IME Edge ALs are much better than Bluemels, just to throw another option in there. There's also a AL56 mudguard that just about covers 700x50s.

If you decide to go with SpeedRockers instead of Bluemels, this is some over 43mm GravelKings. No rattles and great coverage.

45's will be fine. I had 65mm guards on my Longitude for commuting, it had 2.8+ (70mm?) tyres on it, and I never got wet from any side spray

I think it will be too tight. The maker says max 37mm

https://www.sks-germany.com/en/products/bluemels-cable-set/

These are the Edge Aluminum 56s on Conti 700*42s.

It'll depend how much space there is for the guard above the tyre. If there's not much space the minimal gap at the sides plus the bit of flex you get from Bluemels might be an issue. The further above the tyre the guard can go the less of an issue that 3mm difference will be.

IME the chromoplastic guards will crack eventually. I've got Kinesis alu guards on my bikes now.

On the topic of mudguards.

Is there a modern alternative to P-clips? I had no issues with them on steel frames with round tubes, but looking for a new road frameset and a few I like don't have guard mounts which is a dealbreaker.

Does anything exist that can be ziptied to a carbon fork?