I use Vodafone HSDPA in London and the South East. It's been great with the oqo. mostly I don't need to extend the antenna, but when you've only got one bar it can make a difference. When you get full HSDPA the speed is amazing - rivals my 2mb ADSL.
I had Vista ultimate, which I 'upgraded' to XP Tablet. The speed increase is noticeable. But I suffered from the oqo manager problem where the wireless dashboard didn't recognise the wifi or WWAN hardware. This meant I couldn't tum the radios off when not in use. The fix was posted here:
http://www.oqotalk.com/index.php/topic,1892.msg13562.html#newStill can't turn off the WWAN, but there should be an official release from oqo soon. This only affects models when you've re-installed an OS from original disks (not oqo restore disks).
I would recommend the HSDPA version in the Uk, but with XP tablet.