^ Re your Carminas, I'm a 10.5D TTS, 10D in the Barrie, a 9.5UK in most Carminas, but took a 9UK for the double monks since I wear them with loafer socks/no socks. Some people do that -- it's up to personal preference.
Glad to hear your Oxford rivet sizing experiment worked out. Mine did wind up being cut slightly slimmer than my other new rivets (and I got my Oxford rivets a while ago). I think lighter fabrics just make up a big snugger, like the linen for Walts.