In reply to Indy:
Not suitable. From the roundabout at Shrivenham to Swindon it's a heavily used 2 lane roud with HGV's and all sorts. No pedestrian pavement until you get right into Swindon. I beleive its seen it's fair share of acciedents since it's posted 50 mph for most of the way (rather than the natial speed limit for an out-of-town road).
very occasionally I see a cyclist on this road and I cringe and hope they survive every time. Certainly not a runners road.
the back roads between Shrivenham and Chiseldon (Hinton Parva, Bishopstone) are much friendlier, but you'd still need hi-vis at rush hours.
Where are youa actually staying?