2Donkeys
The real question, I think, is which is more applicable to a *PPL* / IR type of flight.
For the UK, I find the IMC Rating entirely adequate for private and business flight. Unless you fly a deiced turbocharged plane, preferably a twin, with oxygen, there are not many journeys where having a full IR will make a flight possible, over the IMC rating. I fly on business quite a bit (very well equipped non turbo, non press, retract SEP) and have not yet seen a contrary to this in the UK although I suppose there must be some and I would be certainly interested in examples.
So, the real use of the IR is for European flying.
Recently I have met quite a lot of people who are building hours for the ATPL and who have done the JAA IR ground school. I have seen the sort of exam questions there are, and the syllabus. I am enough technically minded and would have no problem getting through the stuff I saw but equally it is obvious to me that most of it is not applicable to the most common PPL/IR application i.e. flying around UK and Europe, private and business, in a non-jet non-press aircraft, VFR when possible for the view, IFR/airways when necessary or desired.
As for navigation, owners of modern aircraft practically all use a decent GPS as primary, with VOR/DME. Certainly navigation as taught at PPL level is grossly inadequate for UK/European airspace flying and no doubt this is one reason why most new PPLs pack it in very quickly indeed, but anyone who has a real reason to fly is going to have the incentive to do it properly, and they will see right away the need for an IR and for a plane equipped to go with that - and we aren't talking about a 1970 PA28 with a VOR receiver. The standard of navigation easily achieved with modern kit is way beyond what is taught.
The FAA IR, with an FAA Class 3 medical, is probably "right" for what I believe is the intended usage. I have not seen any evidence from the USA to the contrary. After that, any comparisons become completely irrelevant against varying currency. Currency, especially on type, counts for so much more than what exams you sat a few years ago.
I think it's a pity that there isn't a FAA-like dedicated PPL/IR in Europe.
Of course any commercial operation or ambitions are a different thing, for lots of reasons.