The R8 is all about THAT drivetrain. The BMW/AMG's were good, but they were still boosted engines and all the benefits / compromises that brings. Very little compares to the sensations and responses of a screaming N/A engine, especially when mated to one of the most superb dual clutch transmission that you'll come across. The sounds, sensations and responses are spectacular and a clear step up from the (not dissimilarly priced) AMG GT.
Whilst I've not driven a 991 TT, I did have a 997.2 TT a few years ago which to be frank, I found an extremely boring (if admittedly effective) point and shoot device. I have no doubt a Macca of some sort will be dynamically better than the R8 but I suspect I'd not be able to notice this benefit as much as I do the R8's superior drivetrain. Also, as this is my daily driver the R8 is more appropriate as it'll be better built and have more advanced technology. Ultimately, I didn't really consider a Macca or a 991 TT as a viable option to replace my AMG but I did seriously look at a Ferrari F12 (I even put a deposit on one) but once I'd tried the R8 it was, to me, the better car in almost every way.
I actually intended to swap my AMG GT for a late Gen-1 R8 LMX, just to get that drivetrain. But the interior and tech put me off compared to the über modern AMG so my only way forward was a Gen-2 which has a tremendously modern, minimalistic and yet really luxurious interior (I'm a big fan of the interior which in my opinion leapfrogs everything I've had before).
Quite frankly, the R8's performance is outrageous. Ignore the official 0-60 of 3.2 secs, it's regularly tested at 2.8 and pretty much in line with the 991. Get above 60 and it pulls away from the 991 (by 120mph, it's over a second ahead). If you're used to a car that can accelerate to 60 in high-3's / low 4's like I was, you need to consider that 2.8 seconds is around 25% faster and it feels absolutely gut wrenchingly fast.
Handling wise, this Gen-2 appears an improvement from the LMX I drove, which itself I thought was a very dynamically accomplished car (indeed, it was a drive of a friends earlier R8 V10 a year previous which put the R8 on the map for me). However, I found the Gen-1 a bit understeery on turn-in (much as I did the 997 TT) whereas this Gen-2's totally revised quattro system is initially much better balanced, and then nicely rear biased as you push harder. The Dynamic Steering gets a bit of a hard time in the press but I have no issue with it whatsoever, and I certainly prefer it to the helm in my M6 which was always that car's weak spot for me (and it's certainly nothing like the Dynamic Steering in my RS4 which really isn't great at all). The car rides really well for a car of this type (in fact, really well full stop; it's VERY compliant), body control is great and handling very flat. Dynamically, the Macca's may well be better but honestly, there is nothing wrong with the R8 whatsoever.
Here's a few pics of mine in the relatively subtle black I ended up buying....






