The svt3 goes pretty loud if you set it up right. Start with all the eq flat, ie at 12o'clock and whatever else you do, DON'T use the ultra low switch, it scoops a huge amount out of the mids, robbing the amp of all it's grunt. The ultra high is fine if you like the tone of it.
To get the loudest cleanest sound, set the tube gain on full, the master on full and bring it up to volume on the preamp input gain. I know that sounds odd but it essentially removes the master volume from the picture, you'll notice an svt-vr for example doesn't have one. I'd try not using the -15db switch first up and only use it if you can't stop the pre from clipping. Once you get it sounding loud & clean, start playing wit the controls. If you want more dirt in the sound, turn the master down and the pre gain up. Don't add any more bass than you need as it uses lots of power from the amp and reduces it's headroom, same as any amp. It's best to set the eq with your band, it's easy to get it wrong on your own. With the lows in particular, start with obviously not enuff and slowly add in bottom end until you have just enough to sound good.
Personally, through a modern cab I hate the tone of the graphic eq, very 'solid state' sounding, bright and hard even with all the sliders flat. You might not notice it thru an 810. If you set the gain as I suggest you won't need the extra gain in the graphic to get the amp to produce it's full output, not unless you have a bass with an incredibly low output. You mentioned that you can make the clip light come on so you should be fine without it. IMO/IME etc and assuming the amp is healthy...
