In a monobath, development time is affected more than fixing time by temperature, but fixing time is affected more by agitation.
If you look up the long monobath thread, where I discussed a number of my own tests, I think I posted at some point that I thought it was good to use low agitation at the beginning during the (mostly) development phase, and more agitation later during the (mostly) fixing phase.
You could tweak the variables of temperature and agitation, I suppose, to create different effects. Bear in mind that silver plating out onto the neg during the fixing phase will increase highlight density.