I used performance mode about three times, seeing what the difference was on a straight away, another racing another Roadster in a quick sprint and pitching the back end out to do a comparison between how fast the back end will snap loose with traction control off. I'm not going to use it any more and don't see a huge difference between driving in std. mode and performance. Where you get the most performance is when you charge in performance, then switch to performance and immediately use performance mode. I believe the top 5% is its peak performance if I recall from a Telsa technician, that's where they get their 3.7 and 3.9 zero to sixty numbers. Charging in performance mode charges the pack up to its full 100% capacity so you can pull the most amps from it. Std. mode charges up to 80-87% of the pack's capacity. 100% charges stress the battery pack's cells hence why I charge in Std. Mode and use Range mode (on 220v) every now to balance the pack faster, if it needs it, and also to keep an eye on and see what my true range / health of the pack is. That's why if you let your pack sit in 100% a range mode charge it bleeds the battery down to 85% rapidly, also that top drop of the battery curve is very fast from 85-100% so you don't get that much bang for your buck there in terms of range and health.
The downside of the performance mode is that it adds extra stress to the battery pack for that it allows the highest amperage draw from the pack. I really wouldn't use performance mode below 60-70% due to the higher stresses of the cells. Both std. mode and range mode regulate it to a conservative level/draw.
I also would strongly keep away of driving in performance mode, you're looking at prematurely degrading your battery pack and range over time. There's a Roadster out there that does this, its always in performance mode and every stop/go the accelerator is pegged. I believe it has somewhere around 10k-20k on the odometer and is only getting around 100-110 ideal miles when charging. Unless you have tons of $$ to constantly replace the battery pack I don't recommend it.