I currently own an SWR SM-500 bass head, playing through a Goliath III 4x10 and a Son Of Bertha 1x15. It's a good setup, with good volume and nice clean tone, but I'm looking for some of that fabled Ampeg growl. I played through a buddies SVT 3-Pro, and the growl was definitely wonderful to my ears, and has given me a bad case of GAS. I want to keep my present speaker cabinets, so I would be replacing the head only. I don't think the SVT 3-Pro has enough power for my taste. The SVT 4-Pro definitely has the headroom, but does it sound similar to the 3? I'm not worried about the power rating on the SVT Classic, as I've found tube amps seem to push really hard given their apparently lower wattage ratings. I have not had a chance to listen to either head with my cabinet setup, but I was hoping to get some preliminary feedback from those of you who have experience with either of these heads. Any alternative suggestions would also be appreciated.