Hi, i dont know exactly what route you are planning to take to Snett, but i used to work alot in Stevenage and live near Snet in Norwich, i know its not a great route by bike but by car its the most direct and quickest, Stevenage, Baldock, Royston A505 past Duxford to the A11 short burst of the A14 back on to the A11 and carry on past Barton Mills, Thetford and Snet is about 10 miles from there, by car early in the morning it was'nt to hard to do it in about an hour and a half at a decent speed
hope this is of some help to ya