I've confronted this issue a few times (not ERII, but various dignatories from assorted countries) and the answer tends to be that being noticeable is not an asset. Everyone present is trying to ensure that event is successful (usually understood as meaning that the host or guest of honour finishes the event sober, satisfied and on time) which normally means that those who stand out are almost invariably perceived as detracting from the occasion rather than enhancing it. This is why everyone is dressed conservatively, except when wearing either national costume or a uniform.
After all, the guest of honour will barely remember the occasion and in this case isn't likely to back for a while, but you're reasonably likely to be meeting other guests at the event in the future. You might not want them to remember you as someone who stood out for his egregious appearance.
I would tend to choose a simple dress watch (in my case generally a 38mm RG Omega time-only handwind from the early 1950s), because it neither overwhelms nor detracts from a good suit, ties and shining shoes. Obviously, if I had a Simplicity or something of that calibre I'd always choose it, but regrettably my choices are slightly more restricted. I could envisage myself wearing a classic AP/VC YG skeleton, but that would be very daring for such an occasion.
Conor