Definitely try out all of them, preferably with your own equipment or duplicates. I have the SVT 4 Pro running through a 410 HLF and a 1x15, and it gives a wide range of sound options and plenty of headroom. A good friend runs the same head through the 810 and he loves it (I've heard it and I like it too). Something to mess with - the 4 Pro's sound varies greatly when you change the mid EQ knob setting. I would assume similar things from any Ampeg head, but I'm not sure. By changing just my mid knob, I can go from slap/funk type tone, to a rumble that just sits under the band, to a real aggressive edgy sound that cuts through at lower volumes. This all can be modified by the bass settings even more. One more thing - the dB cut switch (which many assume is just for active basses) is designed so that you can get the gain knob close to maximum. If it doesn't flash the LED with the switch on, turn it off. Otherwise you're missing some of the huge power that this amp has. Once that's set, then play with your master volume and other crap. This amp really runs best with the gain set pretty high, so like if you slap a low E too hard it will flash but doesn't otherwise. I have a bass with active pickups and I run with the switch off to be able to achieve this level. Have fun experimenting! The built-in compressor is pretty good also.