What the XP test shows is that so-called "low flow" blocks need just as strong, if not stronger, pumps than the much lamented "US-style high flow" blocks, in order to achieve their best performance.
The shape of the Swiftech MCW6000's performance vs flow curve would appear to be a better overall solution for the truly "low-flow" scenarios (<0.3gpm) than any of the so-called low-flow optimised blocks. The MCW6000 is also significantly less restrictive, so in super-restricted setups (i.e. Eheim 1046's with 6-8mm ID tubing) it will offer better performance from the radiator too when matched with any given centrifugal pump.
Where the XP's very marginal performance benefit lies is in the rather narrow range of 0.3-0.6gpm, and even then I would hazard a guess that the MCW6000 would be a better solution on the basis of radiator performance. Really need to get Phaestus to show some 0.25gpm results for the MCW6000. I reckon it would be in front of the XP in the 0.25-0.5gpm range as well.
So where does that leave the "low flow" argument? On one hand we have the MCW6000 offering a better solution for the super-restricted setups that the low-flow proponents argue for. On the other hand, in order to get above what the MCW6000 can offer you start to tread into the realm of requiring the powerful and higher pressure head pumps, where you then hit an increasing number of competitive, and even superior, "high flow" style designs such as Storm, Cascade, White Water, RBX with #5 nozzle, and still the MCW6000 hangs in for a fair while too once we factor in their lower pressure drop, not to mention the better radiator performance as a result.
The "low flow" blocks are no different to most of the "high flow" blocks. They still require big and powerful V8's to get the most out of them. One could argue that about the only difference is the width of the tyres, with the "high flow" blocks allowing more contact patch to get the power down to the ground.
