Tom,
you will be able to speed up your work (or compute more alternatives) if you can run your project on a computing cluster, maybe at a university or research institute ?
Some info here:
https://grasswiki.osgeo.org/wiki/Parallel_GRASS_jobs
https://courses.neteler.org/building-a-cluster-for-grass-gis-and-other-software-from-the-osgeo-stack/
http://gfzpublic.gfz-potsdam.de/pubman/item/escidoc:100071:1/component/escidoc:100070/5_GISDAY-2012_loewe_thaler_State_of_the_Cluster_bib.pdf%3Bjsessionid=87D8757B6257885C605BFDC531F067A3 (-> slide 20 gives an overview over the time saved by going parallel).
Good luck with your project,
peter
<peter.loewe@gmx.de>