bedford?!?

B645 out of Higham Ferrers to St Neots is a cracking road, with a nice mix of bends and some fast straight bits. You could turn either north or south of Kimbolton and follow the B660 either to Bedford (south) or Peterborough (north). I'd say go north because the new 50 limit applies all the way south, but it can still be a good road at those speeds if you just want to learn lines through corners etc. The fast fun bit goes north though.

If you carry on up the B660 you can make your way to Ramsey, and from there down to St Ives and on to Biggleswade. There's a good selection of roads there too.

For a good half a days ride-out you have to take in the A507 from Baldock to Buntingford and then head nroth up the A10 for a few miles and grab a bite to eat at the Silver Ball Cafe just outside Royston. The A507 is sublime - that, the B645 and the B660 are three of the best roads in Britain and they're right on my doorstep.

Now that you mention it....
The run from Horton to Whipsnade is quite a goodin

And The road from Baldock to Buntingford is great. Its nice and open, so you can see if there is any traffic up ahead. Smooth road aswell