Best compression = much slower decompression but if I change compression method to not be solid, it will unpack preview pics in the beginning definitely faster in price of slightly bigger size.
"Also, like i've said in past, maybe losslessly compress all png's."
I did it in past after you suggested it, but it only increased compilation time, where the size was the same, and unpacking speed wasn't noticable changed.
It also takes 4 x more time to compile the installer, but that's minor problem :)