The last bit of really pretty countryside before you get to London is the Chilterns. Although your route joining the Thames at Streatly makes sense in terms of directness and elevation (or lack of) if you have the time and legs I would suggest looking for a route through the small Chilterns lanes just a bit to the north. The LFGSS Hard Day Out rote regularly uses these lanes - see https://www.lfgss.com/events/4406/ and if you do go that way and are anywhere near the Blue Tin Cafe (Wed-Sat only) it's worth a stop https://www.bluetinproduce.co.uk/coffee-bar/ .
Happy to give specific route suggestions through the Chilterns, but plenty of others will have ridden there and will be able to help with specifics too if you do decide on that small detour.
The last bit of really pretty countryside before you get to London is the Chilterns. Although your route joining the Thames at Streatly makes sense in terms of directness and elevation (or lack of) if you have the time and legs I would suggest looking for a route through the small Chilterns lanes just a bit to the north. The LFGSS Hard Day Out rote regularly uses these lanes - see https://www.lfgss.com/events/4406/ and if you do go that way and are anywhere near the Blue Tin Cafe (Wed-Sat only) it's worth a stop https://www.bluetinproduce.co.uk/coffee-bar/ .
Happy to give specific route suggestions through the Chilterns, but plenty of others will have ridden there and will be able to help with specifics too if you do decide on that small detour.