Dunc - I had similar thoughts to you. I've tried several of the 'lightweight but loud combos' and not liked any of them particularly. Markbass, Fender Rumble etc. Either not light enough, not loud enough or I don't like the tone. I have pretty much abandoned the idea of getting one, despite how convenient it would be.
I read the thread about these new Quilter Bass Block 800 heads and decided to take the plunge. Early days but I am very much taken with it. Really tiny - small enough to carry along with something else and not notice it. Under 2kg and extremely small. Great tone, very loud and seem to match nicely with Barefaced cabs - at least the two I have tried. It means my rehearsal carry is now more than 10kg lighter and more streamlined, which was my thwarted aim when looking for a combo. I can use the BF 110 with my quieter band, Supercompact with the rock band. Small gigs, too I would imagine, if I can bear to divorce myself from my beloved Trace Elliot head. I used it at last night's gig with my rock band at pub gig volume, intending to just try it but ended up with it all night.