[Josh Martin]

Grip couldn't go past 100%, it makes no sense... It's probably adrenaline and focus in the race from following someone

[Russell Sobie]

This is a car simulator, mind you. Where AI cars in many sims typically have difficulty ratings well above 100%. No, it doesn't make sense, but it DOES have precedence.

[Ross Macfarlane]

The time gain is totally subjective, really.

When I go onto a server or SRS race, I'll do a handful of laps and begin to see what sort of pace I am looking at as an end result. Most of the time I'm too busy getting blocked or distracted by other cars on track to get to that time. So when I go on to an offline session to try and perfect my lap afterwards, I will be easily faster due to the lack of any outside influence.
Of course, others will enter a server and take small subconscious queues from other cars on track and begin to build upon their knowledge of how to go faster in that car on that track. Totally understandable.
When I used to race on a sim without a live delta, I would use the ghost feature of the fastest guys as my reference and safe competition on track to push me to go faster. Nowadays with a live delta on AC there is no need for that.

With regards to the AI percentages, difficulty is something that should have that sort of two way scale. 100% is the virtual benchmark for a driver and anything more or less is accepted to meet that driver's ability.

Grip on the other hand, is simply grip. 100% grip is meant to simulate those perfect conditions of a track state where the rubber is laid down nicely and any more rubber would create that 'peeling' and sliding effect which would lose actual grip and time. Any more than 100% grip would just be breaking realism entirely. More grip shouldn't be possible. This sort of full spectrum track progression is near enough impossible to recreate accurately, so AC has gone for that 100% limit and nothing beyond. It simulates the 'Green' State ---> 'Perfect' State spectrum, unlike iRacing which more or less simulates the 'Perfect' State ---> 'Overused' State spectrum. This is considering its tyres have an impact over time and use on the road (but have been totally broken regarding tyre compounds and progression itself. A real joke of a sim).

Anyway, there is more than my 2 cents worth of opinion. The main thing is we're all out there driving and trying our best whether we are driving on 100% grip or 1,000,000% grip.