The route I did down to Compton Abbas yesterday would actually be quite suitble.
The roads would be suitable but interesting and it's a nice destination for lunch.
It was about 45 miles from Chippenham (one way).
Obviously it's longer from Swindon, but shorter for people joining at Melksham/Warminster.

I like the Divine cafe too.
It's nice there and there is plenty of parking.
I've been there a few times and the ownders are friendly towards bikers.