Just as per Chyl314's review - there is a plethora of new portals within Kew Garden grounds that could now be added to make the banner more logical. I did the banner in a bit different order by swapping missions 5 and 6 due to lunch break.
There are three parks that are closed at night and two of them have portals inaccessible at night - so plan ahead. This banner, hack-only, is doable in 7h - I decided to capture/glyph hack and field/link as much possible and it took me around 12h. I had massive drift around WTC memorial, took me alone 30 minutes to complete the two missions there, but everything else went smoothly.
I've never had to cross the road so many times to get to a portal. Overall the route is really good and takes one around - definitely shorter than 4h, but prepare to upgrade portals for every first portal of new mission (don't fill all the slots on the last hack of a mission!) and last mission has a "create a field" on last portal that was, at least for me, rather difficult to reach.
So, the banner is now almost complete - the mission 28 is missing.
The museum part is really easy, a lot of waypoints reachable from the same spot. GPS can be a bit difficult to work with indoors, but Wi-Fi is free and helps quite a bit.
Second leg, missions 24-48, which is also not pictured here, takes you through Hyde Park (Albert Memorial, Serpentine, Italian Gardens, Diana Memorial), side streets east of Exhibition Road toward Harrods, along Walton Street and then Fullham Road, only to take you back in front of Natural History Museum/Victoria and Albert and to the finish in front of the South Kensington station.