Being that stockless anchors are not usually used on small boats and certainly are neither very high tech nor sexy, they don't seem to have too much available data or even pull tests done.
But I would say that choosing the correct stockless design is as important as it is for all the mainstream anchors. Example, for my boat:
1. Navy style - ABS requires a 264 lb anchor;
2. AC-14 or Pool - ABS requires only 200 lbs;
3. Posidonia (per Murray's thread) - ABS only requires a 132 lb version.
The Navy is nothing but a pile of deadweight as most likely are the dreadnought, Baldt and Halls. But the others have good burrowing characteristics. The Posidonia is basically a stockless Danforth on steroids.
Granted, an anchor that relies on very heavy weight to be effective is not going to be very welcome on a 30-50 ft cruiser of moderate displacement, but for heavier boats an extra hundred pounds means nothing, and they store so nicely.
Just my opinion... give me another year and perhaps I'll conduct some anchor pull tests on these babies, then we'll combine that with Panope's awesome information.