Well for 200y, pellets are out of the question. 150y on a calm day is possible, but then you have the "hang time" and holdover calculations to contend with.
Depending on what size prey you're hunting, energy requirements determine what ammo should be used. A smaller kill zone is also going to translate to the need for precision accuracy, and unfortunately that means the list of "plug and play" options are real limited.
An Impact would be an option. Do know that higher power introduces nasty problems with harmonics (more pronounced with longer barreled rifles). You can mod the barrels for adding rigidity to lessen these issues, but that depends on your level of skill and willingness to "tune".
I've learned that long range shooting with airguns requires good performing ammo with a lot of power to drive them from a solid barrel system (and not all barrels are created equal). I have two PCPs right now that are definitely capable of hunting at 200y, my Veteran 22 cal is a project that I have spent around 8 months tinkering with shooting 40gr boat tails just under supersonic when maxed out, and my new EVOL 30 which solves for eliminating the majority of harmonic problems out of the box. My 22 with 40gr has more power and shoots flatter when tuned down (0.155 BC) than my 30 ca does maxed out with 62gr Varmint Knockers (0.13 BC @840fps).
Now majority off the shelf airgun slug ammo doesn't perform all that great for me long range. The heavier the better. Anything with a BC under 0.13 and lighter than 40gr winds up drifting in the wind too hard after ~140-150y, but I find that you can mitigate a lot of that wind drift in 30 cal with ammo weighing 60gr or more (these 40gr Griffin slugs have almost no drift whatsoever at 300y).
If you want really flat, find a good .257 (make sure you research problems with some that are on the market though). Otherwise, my votes are EVOL 30, Impact 30 (or .22 with 40gr), Just make sure whatever it is has the power to shoot whatever ammo is appropriate (no less than 0.13 BC for accuracy at 200y). I'd consider identifying the projectile first, then matching a rifle to the projectile.