[hamei]

(I can confirm that in PROM the VGA signal is 75Hz, and after boot it goes down to 60Hz.)

Someone did that, and it wasn't easy, and you'll want to fix it as soon as possible because the prom is similar to bios on an x86 machine, when the operating system goes to poop you can almost always get into the box from the prom. It is supposed to and stock it most certainly does, drop back to the lowest common denominator. Otherwise it's useless.

As for the rest, that's why 6.3 is preferable :-)  But one thing at least, you didn't have to choose between maintenance and feature stream ...