Cahoot should be 5.6% on todays rates. However bare in mind 5.6% is the headline rate and Cahoot have a lovely policy of assesing your credit rating then applying a certain rate to what your credit rating is. Not many people therefore get the headline rate but do fail to pick up on this till later on in the deal.
Personally you can't go wrong with the Nationwide deal of 6.4% which is the same every borrower and has no set up or closure fees, has no lock in periods, ahs no penalties for repaying early and will even allow you to do partial over repayments to bring the balance down quicker.
I would stick with them,