Well, I have to say that I gave up my Ampeg SVT-III because it never sounded really clean and didn't liked its mids (not to mention the graphic Eq degrade incoming tone). So, despite I didn't tried that portable ampeg, is not odd hear that someone also conplained about distortion from an Ampeg, although I've used some big stacks live and was really pleased about their 8x10 cab. Can only think in poor production control, may be we just had bad luck.
To get the botton end you need, I suggest trying some of those new ported cabs. I love my Epifany 2x10, it goes deeper than the afforementioned ampeg 8x10 and is much louder (sensitivity 102dB@W/m) in a lightweight package (its drivers are neodimium). There are many other brands doing great cabs that our peers here can talk about.
Today I got my self carrying it to every gig I get, even if it doesn't "pay" for it. But, you know? If the money is short, my pleasure to play and be heard can't be compromised. It would be a second displeasure...