I will have to disagree about the avt series. It is actually the worst sounding marshall series i have ever heard. The valvestates are far superior imo and even the new mgs look promising.
I myself own a 6100, a 2466 and a 1959SLP RI and when i can't crank them i use a boost of course and an eq in the loop. It is very effective and you can get better tone than any solid state series imo. sorry, i haven't heard the class 5 (though you might want to check the jet city 20 if you go low wattage route)