I tend to work with EDM, and then after that it's rock and acoustic. The low end 'should' be fine with the KH310, looking at the specs.
I do have an Adam T10s, that whilst is in a different class could be put into use if necessary (although on paper it only goes a few Hz lower). That could then be upgraded in the future.
I guess my thinking is that the KH120s plus KH750 sub come in around £2K whilst the KH310 come in at £3K.
If Hugh is about I know he reviewed the KH120s with the larger sub - given the choice between KH120s and sub or the KH310s he owns, I wonder what he would buy??
I suspect there are more differences between the 120s and the 310s than bass extension - I would expect the more expensive speakers to have more clarity, better dynamics, better imaging and clearer / more realistic tone colours. I haven’t heard the 310s, but that what more expensive speakers tend to have.