Your numbers for the 39gr BK and 40gr Vmax are quite a ways off from what I get when I run those same numbers. I got 14.86in of drift
The new 53gr Vmax with .290 BC will certainly close the gap on the .204 vs .223 debate.
I should have said that I ran those calculations at 7000 ft. At lower altitude there will be more drift (I get around 14" or so at 500 ft). I just checked, and those numbers were actually from the pointblank ballistics program, not JBM. They are still fairly close, and certainly you can compare the relative drifts with the same input variables.
I also picked up some of the .223 V-max 53 gr. I hope the .290 BC is as advertised. The bullet certainly looks like it should work out - We'll see.
If you like your hunting rifle, you can keep your hunting rifle.
The .204 shooting 39-40gr bullets will out perform the .223 shooting 40-50gr's. The new 53gr V-Max need a 1:12 or tighter from my experience and costly if your not hand loading since Hornady is the only one loading them.
I own variations of both .20 Practical and .223AI and reach for my .20 Practical more often then not, love the low recoil, even though my .223AI has a break. Both are PD slayers out to 500 yards.
Both rounds will be great for you. I've shot both out to 300yds (the .223 much longer, but I'm confident the 204 would keep up, I've just never had the chance to push it) If your aware of what each round will do, and you already have a deer rifle, it really comes down to the rifle itself. They're both great for little critters, neither has the recoil of a 243, it's more a matter of load vs rifle weight (or either could be fitted with a break, making even a super light recoil like a pellet Bullet selection is really the only big difference. I say find the least expencive rifle that will meet your accuracy needs of either cal. Worry more about the gun, you've already narrowed down the cal selection as much as you really need to.
I like things that go "bang"... I love things that go "BOOM!"
Most all of my shooting has been at prairie dogs. I only shoot targets off a bench rest to develope reloads and check a rifles accuracy. If you are comming out to prairie dog country have a accurate .204 Ruger rifle. I started shooting p dogs in 1949 with a 22 RF rifle. I dont know if there is a perfict p dog rifle but I keep trying to find it. Sofar I have shot them with 17 HM2, 17 HMR, 17 Fireball, 17 Rem, 204 Ruger, 22 RF, 22 WMR, 22 Hornet, 221 Fireball, 222 Rem, 223 Rem, 22-250 Rem, 220 Swift, 243 Win, and deer-elk rifles. Except the Hornet, the centerfire p dog rifles will shoot sub .75 inch 100 Yd groups. For me, the 204 Ruger, 17 Fireball, and 17 HMR rifles will cover most my p dog shooting. But when I can get an accurate Hornady 17 Hornet rifle Ill give it a tryout. It must have a low muzzle blast , flat shooting out 175 yards ,could be a fine round for spring p dog pup shooting. I have two accurate bolt action 223 Rem rifles but dont use them since getting the 204 rifle.
+1 for the .223rem I have a rem700 and an ar15 both chambered for it. I don't have much experience with the 204 but i can tell you the muzzle report is much much more than that of a .223. I'm on a budget and for me .223 is where it's at. I can buy ammo just about anywhere and it's cheaper than 204. I run 55gr v-max out of both of mine and the accuracy is awesome!!! My ar will shoot one ragged hole at 100yd, and 3/4-1"at 200, i can hit standard size clay pigeons at 400yd with either of them. For me .223 is ideal, if i were shooting past 3-400yd all the time or had many many more shot opportunities at those distances I'd consider the .204 but, for my area the .223 can't be beat.