Porker:

Impressive driving and good times in these conditions! How do you rate the 991 RS on the Nordschleife? I assume it's quite a bit easier to go fast with it?

Tricky question. Doing a fast lap in the 997.1 GT3 is a hard job, very physical. You are sometimes driving the car with just one hand on the steering wheel thru corners to get a good shift point. The timing of the shifting is so important and if you loose concentration for just a short time you pay for it. If you miss a shift  in the 997 your lap is wasted - regarding to laptime. When going faster in the 997 at for instance the jump at Schwedencreutz you might end up in a situation where there is no time left for downshifting or even proper braking. (Of course this is also something you must train and get used to.)

The 991 RS's limit is on a different scale compared to the 997.1 GT3. Naturally.
The PDK helps you doing shifts in situatiuon where it maybe would have been impossible with the manual.
Especially good in a dry/wet situation.

I would say that the 991 RS is much safer to go fast in on the Nordschleife than the 997.1 GT3.
You can feel that the car is more composed and stable in a lot of parts of the track where the 997.1 is more nervous.

I'm a carefull driver, I try not to overdrive and I try to build speed from below. It takes it's time but it is rewarding.
When I signed up for the RS I actually looked for a 997.2 RS or a 4.0 RS because I felt I needed a new toy and that I wanted a slightly better car to be able to go faster without necessary drive to close to the limit - my limit.

Which one is the funnest to drive?

Very difficult to say... It is like comparing apples to oranges. I know the 997 GT3 inside out. Driven it a lot. We are best friends. Amazing capable car. 
The RS: A new friend which I'm just are in the beginning of, what I hope, will be a rewarding friendship. I don't know the car good enough yet. All I can say for the moment  is that I'm faster in it.
But judging from following Peter Trakcar and his adventures with his RS I will probably end up loving and enjoying this car to.