Originally Posted by
cny-bikeman
Chain Maintenance
A megarange
will require a different derailleur, as it has to be capable of handling the larger rear cog and wrapping more chain. We can't tell you if you need a megarange - depends on terrain, load and fitness.
Seven speed may not fit into your bike so that you have enough room between small cog and dropout.
He's right it "may not" but it most likely will, standard spacing for both 6 and 7 is 126mm.