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Much like @MuswellGreg's experience really. The first bit was busy, a lot of it was semi-suburban though so traffic speeds were a bit lower. It wasn't so bad in a group.
After Newbury it was very quiet and scenic, albeit the traffic you did encounter was much faster - lots of national limit sections IIRC. It was pleasant enough as A-roads go!
The second route does look a good one though (also 1000ft less climbing)
I've done it down the A329/A327, the A4, then the A420 from Chippenham for a bit, diverting onto the Railway Path at the end (there's no really pleasant route into Bristol). Probably too many A-roads for your purposes.
https://ridewithgps.com/routes/6040705
Here's a more back-laney route posted on here (Edit: just saw that's the Farnborough one you mentioned):
https://ridewithgps.com/routes/172373