I'd look at Retumbo, H1000, and H4831. I prefer Extreme powders.
Check out the online Hodgdon data.
For the Varmint load, the 110 tnt will shoot flatter than a .22-250, and hit twice as hard. This demonstrates the futility of using such an overbore round for varmints, as you are burning 3-4 times the powder. But hey, I use this bullet in my 7 WSM, and it does rabbits like some rounds do prairie dogs. Having fun doesn't always have to make sense.
For the other two rounds, I'd pick a Berger in 168 or 180, or a Hornady A-max in 162. I think the 180 Berger would be best. This round will be good for targets, and Bergers are used for hunting too.
DRT is also a function of where you hit them, not just what you hit them with. That is why some long range people favor a high shoulder shot that breaks both shoulders. The animal is often instantly dead, and if not, it will be by the time you walk up to it.