If you change at Reading you can change to the train to Bedwyn which is a nice ride to the start. Bit of road, some nice off-road (Savernake Forest, Treacle Bolly), and only one busy climb upto the start of the Ridgeway from Marlbrough.
Makes it logistically easy too as you’d get a return to Reading, single to Bedwyn, then ride back on the Thames path from Gorring to to Reading.
I can recommend a slab of the Court Hill Center flapjack in your pocket to get you through the last 25 miles into Reading, it’s propper flapjack that turns a paper bag seethrough. They do simple food, ice creams, cake etc too. We had lunch there although it’s a way into the ride so take snacks and the lunch menu is nothing special (£7.50 for a jacket potato and beans).