I'm not sure I agree that stainless is unsuitable, though I feel that steel that stresses toughness (as few stainless types do) would be better.
A few years back I read a review of a Katana-like "Combat Sword" in tactical knives. The blade was ATS-34 and held up nicely to the reviewer's abuse. This convinced me to use the same ATS-34 I'd used in smaller blades for a pattern of "Combat Machete" I had been working on. This is the result:
The blade is 15", not quite sword length, and fully flat-ground from 3/16" stock because I wanted to balance strength and weight with a machete's handling and geometry (as much as possible, anyhow). The idea was to make a tool that would serve as heavy but tough machete 99% of the time, but should the user ever (for some bizarre reason) find himself in a close engagement where a firearm was unavailable or inappropriate, would give a massive advantage versus the average "combat" knife.
Anyhow, I tested this blade by hacking down several saplings, chopping through a hardwood 4"x4", cutting stacks of coins (6 pennies was my record, but I'll bet someone with better control could do 10 - it's hard for me to swing hard and hit a penny squarely!), and finally chopping into aluminum barstock. The barstock caused edge deformation but no chipping. The other tests only caused some dulling. The heat-treatment was by Texas Knifemaker's Supply, who seem to treat ATS-34 a little softer than the factory standard (60-61Rc), which probably accounts for this performance.
Now, that's not quite sword length, and I never parried another piece of steel with it, but I do feel from my experience that ATS-34 is not "too brittle" to be used in a sword (especially at greater thickness than my fully-ground 3/16"). Not as good a choice as 5160, to be sure, but if it's what you have on hand and are comfortable with, I think it should do fine.
Little Bear Knives