Can I suggest that the roles of R1 and MR have absolutely nothing in common, except for the requirment to have a big aeroplane with lots of back seats ? So lets not have a discussion about apples and lumps of coal.
Can I go on to suggest that the absolutely convincing arguement for the UK buying into RJ is that we then have a tactical collector (in one particular niche segment of the ISTAR spectrum) that is pretty much the same as that used by our principal current and future ally? If you cannot work out why this is a good idea then I can't help you.
Can I finally sugget this this is a Good Thing? If you do not not believe this then I sugget you talk to the RN, who made the commonsensical decision some decades ago to buy a US sensor, and have benefited hugely since.
IMHO (as a useless civvie who is not worthy even to be used as a standby sex toy by the two or even one-winged gods of the RAF) over the three decades I've known what they do, 51 Sqn have done a great job with sometimes marginal kit, RJ should put them into a whole new game.
SO stop w@nking about airframe numbers, think what the sensor is for, and be happy.
Room40