Updated yesterday to XXJM2, and it made the phone faster, the GPS faster, now the GPS works and finds my location just by using WiFi, and the new firmware comes with an app killer widget. This killer comes with a widget that shows how many tasks are running, and you can kill them one by one. However, only apps that you have startet are mentioned, so you do not get the problem of killing important processes like alarms (a common problem with many taskkillers).
The battery is also improved. Now it's 14 hrs since charging, and I still have 83% left. So it has used 17% in 14 hrs - if that continues, it will last for 82 hours (I know that is not realistic, but still it is good).
I updated via Odin, and used the 512 pit file as mentioned above.