29.8/30.0mm are both fine - nothing like enough difference to matter
Keep that original safe too!
FWIW 0.2mm did make a difference on my old On-One which was 29.8mm... I used a 30.0mm clamp with a half circumference homemade shim to ease tightening
PARTS FOR SALE:
vintage Brooks Professional saddle | Specialized FACT CX fork | Columbus fork | Reynolds 531 fork | Avid Arch Rival v-brakes | various 700c, 27" and 26" wheels | vintage Weco hubs (fixed/freewheel) | vintage Raleigh ladies frames + lots more!