You're right, it's possible to play with partitions, and make some differents configurations.|
I have modified sys_partition.fex and increase all the patitions (without boot), and sda1 is smaller, because I don't use it.
But at the first boot, all my personals apps (I put them in /ANDROID/android/out/target/product/sugar-lemaker/system/preinstall) are more faster installed.
I have tried a Benchmark before and after the hack (with AnTuTu). It was 10500 Pts, and now it's 12000 Pts. So it's a little difference, but a little more
Maybe your SD card is faster than mine, because I see the change in normal use!
Anyway, thanks for your contribution