From my memory of visiting the rellies in King's Lynn from East London I used to head up to Braintree (boring bit of either M11 to Stansted then A120 across to Braintree, or up the A12 to Whitham then out the back road). From Braintree up to Halstead, then Long Melford - pleasant enough ARoads but not that many good blast opportunities, then into Bury. Get through Bury and head up to Elveden (notthe mai road to Thetford) on b roads under A11 and up through Thetford chase. Roads here great blatting through the forest. Past Centre parcs up to Brandon, head out towards Mundfordd but just out of Brandon hook left to Weeting and Methwold then eventually join main road to KL near Wareham. Head on to Stradsett and you can then either go left towards Downham Market or straight on (its a staggered crossroad) to KL and head up A17 (dull). If you head towards Downham dont go into Downham centre but go south to Denver - home of what used to be my favouritest bike dealer Denver M/c's a Ducati dealer - now defunct I think.Go through Denver over the sluice and out on ARoad to Wisbech. Stay on this road through Wisbech (dont stop unless you want to get mugged or marry your cousin) and you will hit the A17 at the Macdonalds past Sutton Bridge. Not sure where in Lincs youre heading but if you re north based then you can blattup the 17 then head upto the A52 breaking off to hubberts Bridge then Langrick Bridge through New York to Horncastle then up over Caistor top .
For the Peterbrough to Super Sausage if you want to avoid dreary dual cariageways then head out on A47 to Leicester. Keepgoing till youget to Uppingham - A47 is an ok fast a road - then head south to Medbourne and Market Harborough - a well known twisty bike route. From Harbourough head towards East Farndon, Clipston , Naseby (battle of) Cold Ashby into Watford and drop under M1 and onto A5 near Watford Gap. Straight run downA5 to SSausage.
Hope that gives you some ideas.....enjoy the ride whatever you do.