I don't use 7th under about 80 mph, which means quite a bit of shifting back to 6th on becalmed freeway driving. I found that I had to pay attention to avoid shifting from 7th to 4th when I want to get 6th. If you do end up in 4th at about 80 mph you won't overrev the engine, but it's still disconcerting. I found a technique that reliably works for me: let the spring action on the shift lever guide you naturally into the 3rd - 4th plane and then toggle to the right and back into 6th. It becomes one fluid motion after a little practice.

The manual is generally sweet and pleasant, but it took me a while to get used to its longish throws, coming from a GT2. For me the GT2 action is completely natural, the 991 isn't. I've never, from the first moment, had to think about shifting the GT2 and never picked the wrong gear, whereas the 991 MT requires more concentration and I've missed a few of those 7th to 6th shifts, ending up in 4th. I've always caught it right away before getting the engine revved up, but it bugs me that my shifts aren't prefect all the time. This experience makes me a little less confident in my other shifts as well. Have never had that problem in the GT2.

 

It may help to set your multi function display to show the gear that you are in as its much easier to read than the regular gear indicator.

As mentioned the fact that the car won't let you stall it is a huge plus while getting comfortable with the manual.

Disable the engine start/stop feature.

Enjoy, it's a great gearbox once you get acclimated.