Words and phrases used to modify comparative forms:
Formal
A big difference —> decidedly, a good deal, significantly, distinctly
A small difference —> somewhat, barely, marginally
eg. significantly more intelligent, marginally higher
Informal
A big difference —> way, loads, miles, not half as … as, not anywhere near as … as
A small difference —> a tiny bit, much the same, pretty much the same, more or less the same
eg. not half as expensive as, a tiny bit longer