Thanks all, I've indicated a few answers and additional info which might help.
will you be showing these on the same url? Y
are there any other regional differences? N
how do you intend to identify US and UK visitors? Analytics
what do you have planned for non-US/non-UK visitors? This is a US focussed project.
vincevincevince: It should be simple enough to do; you need an IP database. As the UK has a much smaller number of IP blocks, just get the UK list. Run a check on page load, and set a cookie to indicate what you just learned (check on privacy requirements here). - would this potentially be a problem due to new cookie law?
g1smd: thanks for the input on the numbers - taken note