The models mentioned are industrial, and generally larger, stronger and faster in every respect. There's a blog post on someone fixing up and old
Singer 281, which looks like it has lots of harp space too. Some of the old industrials have caught my eye, particularly one in a domestic looking cabinet. It looks like it can fit in my house with out taking up too much space.
The old cast iron domestic models have generous harp space, at least compared to the average dometic models of today. There are lots of QE, and long models and it's hard to generalize. Model 15, 27, 66 and 201 are about the same, but I haven't had the tape measure out. These are easy to find and well worth the effort to fix up; I have a 201 in a small table, it's a joy to work on compared to any model out there. I don't free motion much, but sewing jackets and coats is a joy on it.