Google.com / Google.co.uk

widgit.com / widgit.co.uk how to list higher

[Think]

OK, in brief, we run ONE website, have around 8 domains (mis-spelling and other variants both .co.uk's and .com's).
The main site and the inbound linking structure is all to widgit.co.uk (our one website).
The main URL and most of the other redirected URLs are on UK servers, 3 however that point to the .co.uk site are on German servers where the domains were first registered.

OK, now I have set the scene, heres the question.:-

Both our and our competitors site have PR5's have circa 60 inbound links each, offer the same keywords etc, both use H1's/H3's etc BUT while we compete in positions 1-4 in google.co.uk when we search in google.com they stay in positions 1-6, we move to around 25.
They use a .com site, we use a .co.uk

I can't get my head around it, they do not appear to be doing anything unethical (nor are we). Also if we search in other SE we get a similar result.

Would you recommend we move one of our .com's to a US server and build inbound links to this one. The thing is we do not want to create several sites. We want one site with one lot of content, if people use any of our other domains then they still get the same content the address bar however keeps the reference to the domain where they entered.

We only target the UK market, this being the reason we picked the .co.uk to run with but as many people defalt to using the Google.com SE and even if you pick UK it still initially defaults to the .com results so we feel we maybe loosing out.

Recommendations please.