Roadster can definitely get as heavy and saturated as you will EVER need, trust me on that (and of course a Tube Screamer-type pedal is mandatory IMO, not for adding any extra drive but just for thinning some of the lows before the input signal to tighten them up) - I've played them and heard them (both live and in clips) multiple times to be quite certain of this, and I up until recently owned 2 ch. Dual Rec that was sweet except for the amount of fizz it would have at gain levels sufficient for metal (meaning, when the palm mutes actually had sustain beyond the initial attack, and I'm talking more fizz than would be present in comparable high-gain amps, because of course some fizz is expected). Here's a clip demonstrating what I mean, I eq'ed out as much of the fizz as I thought I could get away with, but some still remains (however, I don't like the sound of overly processed tones, so I didn't want to cut any more)
http://dl.getdropbox.com/u/332050/AoF%20Rough%20GTRS.mp3
And according to owners and a guy I spoke to at Mesa, the Roadster is voiced slightly darker than the standard Dual/Triple recs, and actually, the reason I sold my 2 ch. was to buy one! (though once I had the money, a bunch of car expenses reared their heads, so it'll be awhile yet :evil: )