Ace,
I've done the SVFR twice, once SE-NW routing Brooklands (nice prominent landmark) - Thorpe interchange M3-M25 (another prominent landmark with Thorpe park easy to spot at 900 feet!) to Ascot racecourse to White Waltham. Following the M25 from Brooklands to Thorpe keeps you clear of Fairoaks ATZ, BTW.
The second time was from Fairoaks, again Thorpe - Ascot and on to Burnham and exit at Beaconsfield. After passing Burnham I was cleared to 1500.
I've not tried from North to South - WCollins makes a good point about the altitude.
Watch your heading and altitude, and give some thought as to what you would do at low level if the donk qui