GB, go with the 12V system. That will do everything you want. You do not need 18V. If the 12V Makita doesn't do it, you're in trouble and need for some cord powered tools.
I have a 12V NiCd System (6271) that works great. I even drill holes in massive stonewalls with that one! No problem at all.
@ Gabby
That's a RC thing. Drill batteries are charged different. I have been racing RC-cars for some years, where the batteries are discharged to their max and then charged with up to 20A. Those batteries could burn from time to time (have seen it 2 times -never my onw ones).
That will not happen to drill batteries.