Well I maybe biased because this is what I wanted to hear but personally I think spot on, particularly the Kissmetrics article from a later response. I have set geo-targeting already and will also sort the HREFLANG tags.
I plan to leave both sites on .com domains - In the UK .com's are just as 'normal' as .co.uk's. All content has been updated to US english and with specific relevant info so I think it's just down to the usual link building and adding content to get it to rank.
I genuinely appreciate all the responses, fantastically useful, thank you!
Mat
