#1
would this head be enough to drive the 4x10 and later on a 1x15 in the same range at full power or do i need the 600head
#2
It can do both, it'll deliver 150W to each of the cabinets.

When you have one cab hooked up, itll be running at 180W.

Gear:
Fender Standard Jazz Bass
Artec Matrix Pedal Tuner
BBE Optostomp
Boss GEB 7
EHX NYC Big Muff
Ashdown MAG C410T-300
Torque T100BX
GAS-ing for:
Boss SYB5
Behringer Intelligate IG9
#4
If you get the 600W head, you'll be running at 300W with one cab and 600W with two cabs

Gear:
Fender Standard Jazz Bass
Artec Matrix Pedal Tuner
BBE Optostomp
Boss GEB 7
EHX NYC Big Muff
Ashdown MAG C410T-300
Torque T100BX
GAS-ing for:
Boss SYB5
Behringer Intelligate IG9
#6
The new MAG cabs handling rating is 450W, their peak is nearer 900W so you wont have to worry about overpowering it as each will only be getting 300W RMS, which is under their handling.

With a 600W amp you wont need to turn it up to full where the worst "peaking" occurs so you will be fine.

Gear:
Fender Standard Jazz Bass
Artec Matrix Pedal Tuner
BBE Optostomp
Boss GEB 7
EHX NYC Big Muff
Ashdown MAG C410T-300
Torque T100BX
GAS-ing for:
Boss SYB5
Behringer Intelligate IG9