i would get in touch with o2 support, i'm with o2 now after ditching vm bb. my attenuation is 23dB up and 43dB down giving me an effective 1.3mb up and 12mb down, my overall line length is around 2.5km (about 1.6 with the crow).
you could also have a look and ask
http://www.beforum.co.uk/index.php, there are some good peeps in there and can give some good advice regarding o2 and be.