The Vintage Rails is a lot lower in output than the Cool Rails; I'm not sure where you got the opposite impression from. The Cool Rails in parallel is still hotter and thicker than the Vintage Rails, and in return the Vintage Rails in series is still quieter and brighter than the Cool Rails (in series). The offset half-rails of the Vintage Rail also mean that in both series and parallel it has a much sharper pick attack than the smoother Cool Rails and the less even power between its coils mean it doesn't cancel hum quite as effectively. A series Vintage Rails is more like a Strat-size equivalent of a Seth Lover (but still brighter), while the parallel Cool Rails is like a Strat Hot Stack with the volume and tone controls both rolled down. You get the Vintage Rails when you specifically want a Strat-like tone with humcancelling and no output drop when bending, but don't want the power of the Hot Stack; you get the Cool Rails when you want a humbucker tone. There's really no point trying to use them in alternative ways to get different sounds out of them. If you like the idea of the Vintage Rails but you want a series humbucker tone, you want the Cool Rails. If someone likes the idea of the Cool Rails but wants a parallel Strat tone, they actually want the Vintage Rails. That's why the two pickups exist as separate products. No matter how you wire them up, neither one of them is able to 'cross over' into the other's territory. The CR is always the humbucker-sounding one and the VR is always the single-sounding one.
As for the SD EQ charts, those are relative charts and quite misleading if you try to pitch them against each other 1:1. For example, in that comparison of the three pickups, those charts don't show you that the Cool Rails and Vintage Rails each sense a much smaller length of string than the Sentient does, giving them both a much brighter and sharper note attack. (Which by full humbucker terms would come across as more treble... like the Sentient has.) It also doesn't indicate the compression (the VR is noticeably more compressed, both in series or parallel, than the other two) or give any indication to the pickups' sensitivity to string spacing and proximity. (The VR is really sensitive to variations in string height, while the Sentient has the most drop-off when bending strings or when the string spacing doesn't line up with the poles.) Lastly, it barely takes output into consideration; if you look up the Invader's EQ chart you'll see it shows it having very low treble, when in reality that pickup's output is so high that even though its treble seems low compared to its bass and middle, in a total sense it still produces a stronger treble signal than any low-output pickup.
We can make this very straight-forward:
If you want a humbucker tone to match with the Nazgul (but in a Strat size), get the Cool Rails.
If you want a hum-cancelling single coil tone to match with the Nazgul, get the Hot Stack.
If you want an actual single coil to match with the Nazgul, get the Quarter Pound.
Leave the Hot Rails for pairing with high-output super-thick humbuckers (e.g. Invader or Black Winter), or as a bridge pickup itself.
Leave the Vintage Rails for pairing with low- or medium-output humbuckers (e.g. Jazz or Cool Rails) or as a slightly smoother middle or bridge option with 'true' single coils. (Yes, even if you wire it up series.)