Just grab a 32T cassette to swap on when you're hitting hills, there's no point going lower chainrings if you're already running 50/34! Big track guy like you should be using 53/39 anyhow!
I run a 32T year round as I'm on 52/36 with lots of rolling terrain and I like hills. I'd probably swap to a 28T if I ever sort some aero wheels for chainganging and such. I have a 'spare' 28T on my turbo and it's not really needed.
I think that's my conclusion - except I seem to recall I accidentally mixed up the 32T and 28T cassettes the once (when I had the Giant and the Trek bikes at the same time) and the Trek wouldn't change gear - it took me a while to figure out the RD on the Trek was short cage and couldn't cope with the dinner plates 32T. So I might actually only be able to get up to 30T on the back with the short cage. Oh god I'm going to be pushing it up Saintbury again first week of March aren't I?
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