What rims do you have? Some wide ones are rated for 23mm tyres. Also the narrower tyres are slightly more aerodynamic. 24mm might not be the worst size.
Also, I would be really keen on any first-hand experience with the Cronos. Got a TT coming. Good roads, but not sweeped, chance of small gravel bits on the shoulders. Worth using them over SCs for race day? My interest comes from their low rolling resistance, rather than weight.
Mercury M5s. They are 25mm at the brake track.
To answer you:
We have used the Cronos thin ones (19?) a lot on the TT bike too and used to use them for RR but switched to Veloflex Records for RR and later the wide profile tyres.
Cronos are good tyres. For us the Cronos punctured a wee bit more than the Veloflex records on the road.
I think the Veloflex Record is slightly better made, but it is also slightly bigger. My son is a junior with gear restrictions. With the Cronos he could run 53X14, with the Veloflex he has to use the 52 in front as they are larger profile.
Running Veloflex Reocrd rear, Vittoria Crono front in this picture: