Whatever you get, if you want it quiet, make sure the barrel is threaded for a moderator. Even a cheap Buck Rail moderator for $30 makes a huge difference.
The AvengeX is probably a decent choice since there are multiple configurations (tactical, bullpup) you might like. Personally I prefer shooting 30 caliber rifles where I can turn down the power if desired. It's fun to shoot slugs and have that "22LR" power on tap that many 30 caliber air rifles have now. 30 caliber limits your options a little on that budget though... you may have to choose between super accurate or super tactical
Question for you: Do you have a PCP air compressor and is that part of your $800 budget as well?
And: What accuracy is acceptable to you? Almost any PCP is "accurate" with the right ammo and within its limitations. There's a few lemons out there, I'm sure. But are you trying to impress other people shooting paper targets hole-in-hole, or does accuracy to you mean hitting a squirrel pretty easily at 75 yards?
I currently have a original 30 cal. FX Crown, which I love, and I agree with your reasoning for the 30 caliber.
However, Im wanting something new, and shorter ....something more practical for both plinking and pest control.
Seems like in order to get a short rifle, dropping down to 25 would be a wise choice, in order to maintain a reasonable FPS.
Even a 22 is a option for me, at this point.
I have 2 inexpensive compressers, but Ive never even used them!
They are still new, in the box.
Im fortunate to have a local company, a few miles away, that will fill my big, 88cf carbon fiber tank up for $10.
The beauty of that, is that their air is high quality, breating air, thats free of moisture.
But I do keep my 2 inexpensive compressors as emergency back up, in case anything happens with my local company.
The Avenge X is a product Im not aware of, so ...after several recomendations, I will certainly do some research on their offerings.
Thanks much to those that responded!