I got a stream suggestion to use cvs-faster-export instead of cvs2git, which does seem faster but it OOMed, but I also had to modify the ,v files to ge cvs2git to actually load the repo, so if I do this for anything more than a one-shot, I'll have to experiment on the best way to do this.
I dunno if there' mush use for this, but I'd probably be willing to setup the stuff to do this semi-regularly if there's want/need.