Hi,
I have thought about this question all the time, and I don't know what's more important.
I have an Ashdown MAG 300H and I use 2 cabinets: MAG 410 and MAG 210. I like the sound, and the head with my 410 sounds good for rehersals, but I leave that cab with my drummer, in his house. I have got now another band, and my MAG 210 don't make the job right, I have to use more than 7/10 and I don't feel pleased. I use the EQ flat, with a little more of mids.
With this, I was thinking on buyng a new head, with 500/600w (matbe Ashdown MAG600?), but I have read that the double of the power isn't the double of the volume, and the difference isn't very much. But if I want more power, I thought that I have to upgrade my cabinets, but I don't have more money to spend... And now I'm thinking if I get a better 210, it is the solution for my problem, that sounds better and loud.
Edit: When I have gigs I normally use the two cabs. I don't want to buy another cab, and I don't have very much to spend, and 3 cabinets are very much for me.
But the main question is: What's more important, head or cabinet?
I'm sorry about my english. I'm portuguese.