Its a constant dilemma
Like other people who replied I have experience of the cars you're interested in. I've been lucky enough to have 6 Porsche's( 911, Cayman S and Boxster S) and 8 BMW Cars (M3's Z4M coupe and M3 CSL) and a TVR
What do you intend to the use the car for?
If it's a daily the M3 E92 is great car, but is very expensive to run, looking at 17-19 mpg around town and 20's on the motorway. Not a problem if your doing low miles, but is a proper pain doing greater than 10k a year and it wears a bit thin putting in over £100 a week in juice. The servicing is expensive even at a decent indie. The V8 M3 is a awesome drivers car, pointy front end and you get use to the RWD and gel with the car very quickly. I would not worry about losing the back end to be honest, the traction control system has different stages and looks after you, you can really drive like an idiot/no talent and still be fine.
I recently acquired the Golf R and I am very pleased with it, but compared to a mid engine'd car like the Boxster, it feels very detached. The Golf R is faster than the Boxster (which I still have, its a 3.4 S 295 BHP version), but the feel, connection, balance and way the Porsche drives is much more engaging, even if you are ultimately going a tad slower in the dry and a lot slower in the wet/damp. The gearbox feels more precise, the steering has greater feel, brakes full of feel. It's a different experience to the Golf R. Which a very capable machine and superb value for money, (even more so tuned), but with M cars and Porsche you get a proper pedigree engine for example( V8, V6 or flat 6), not just something which does the job, is very efficient and easy to extract power from.
I wouldn't be so quick to dismiss a non turbo 911either, it's a common thing on forums to read this, but the 911 C2S was a fantastic car with a manual gearbox and I had some really great drives in the 355 BHP 911 and don't forget none of that power wasted due to great traction as the engine is over the rear wheels, even in the wet
If I was you, I'd be looking at the M4, it's can be tuned fairly easily , is much more modern than the E92 with better mpg too, but still has that classic BMW feel when driving. You know that sharp front end, feeling of loading up the rear and hint of over steer on the exit which is hard to beat.
If the ultimate pace is of the upper most importance I'd stick with the Golf, not much touches it for value for money,0-60 speed from the lights and down a bumpy B road