Dane has asked about mingling bourbons and this is something I still like to do.
Lately, I have been returning to all-straight whiskey mixtures. I still do ones with admixture of Canadian whisky and vodka but I find these lighter versions go well in Manhattans (better often than all-whiskey blends).
Recently I used Beam Black, Virginia Gentleman and Overholt in a 45%, 45%, 10% blend, using the best blend formula of Jos. Fleischman from 1885. It is very good. The strong notes of the Beam whiskeys are displayed but also softened by the good but relatively mild Virginia Gentleman. To do a good blend, you need things that complement. Since Overholt is reasonably pungent and has the Beam taste too (to a degree), I'd have thought adding Overholt would not do much or would take away from the blend. Not true.
You get a depth and flavor with a good mixture that many individual whiskeys won't attain.
I am thinking now that my very flavorful, smoky, earthy Old Weller Antique 107 would work well in a blend. If I had more VG, I might use that, but I don't. I am planning a 1:2 Weller Antique and Forester 100, that might work since Forester is so clean, only lightly smoky and fruity. I have some Forester 100, also from Lee's Discount in Vegas. It is very good, just like the pint of same I bought in Louisville last month.
Next to it was a Bonded Old Forester sporting the now discontinued label. I should have bought that, and still may, to compare to the current 100 but am very happy with the latter.
This current OF 100 doesn't need blending but could still be used with profit in one.
As for WT 101, JBBL and KC, I don't think I would mingle them, even the last two. All I can say is, consider, light and dark, point and counterpoint. Very vigorous bourbons will usually clash.
A wheater and rye recipe is usually a good strategy, as is a low and high proofer.
It is just common sense.
I'd like to reiterate though that I will only do it where the base whiskeys are ordinary or seem lacking in some way. With a superb straight, you don't need to do it.