Regarding the BOAC P&W 707s.
The earliest ones, delivered from 1965 onwards, were all-cargo ones. Boeing never produced a 707 with both the cargo door and RR engines, so BOAC had to go for the 707-320C for these. BOAC had a worldwide all-cargo network across all continents, and these operated those routes.
In fact by the end of 1963 the RR 707 was out of production altogether, so BOAC were forced to go for the P&W model if they wanted more. The last BOAC RR aircraft actually came in early 1963, nearly two years before the first VC10 came in late 1964
Hotel Uniform (G-AWHU) was indeed originally ordered by Saturn, but cancelled before delivery and thus taken new by BOAC in August 1968. It retained its Saturn model number, and I believe it had some flight deck layout differences. In accounting terms it was seen as a replacement for RR 707 G-ARWE, which had been destroyed a couple of months before in the Heathrow accident. G-ATZD came from British Eagle a few months later, after the bankruptcy of that airline. All other P&W aircraft were BOAC orders.
G-AXGW/X were 320C aircraft which came in spring 1970 for the operation of the Tokyo via Anchorage route, which was slightly beyond the capabilities of the existing fleet.
G-AXXY/Z were 320B aircraft which came in Spring 1971, the only ones in the fleet without the cargo door, which gave them a further small range and efficiency advantage, and were ordered for the new Tokyo via Moscow route (the "Russiaway" route), which again was stretching things (especially for a westbound alternate if Moscow became closed in winter weather, I believe they normally filed for Helsinki as the alternate). They were also the first aircraft with IFE, in part because the entire westbound trip Tokyo to London was done in daylight rather than as an overnight sleeping service (and of course because IFE was just coming onto the market then).
The two Tokyo services did not require all four aircraft, in fact two could have just about managed them both, so they did appear on other services from time to time.
The last RR 707 was moved over to the Airtours fleet in 1976, whereas the last P&W aircraft went in 1983, so for the last 7 years the whole remaining BA long-haul 707 operation was with the P&W aircraft.
This thread has some interesting comments from the time.
http://www.pprune.org/aviation-histo...dc8-707-a.html