good route I have done many times but I think you missed one of the best bits by using the A338 dual carraige way from Hurn up to the Verwood turn off at Ringwood, if you take the Matchams Lane - Hurn road that runs parallel to the A338 you would find it resurfaced and very sweet bit of road there is a 40 limit though ;-) if you follow me.
An excellent circuit, takes spectacular Dorset Scenery, and a mixture of good straights and sweeping bends with bendy stuff at Zigzag Hill. Beware of oncoming in centre of road at Zigzag. Speed cameras @ verwood are well signed and obvious. Occasional police bikes around straights approaching zigzag and on A31. Note: they are particularly sarcastic.