UNV has rentals which is really good if you want to try that route and I would suggest trying that route if you don't have any other way to get to see any thermal. I 'work' for their competitor, Third Coast Thermal as a pro staff sort of guy and get to try out a variety of thermal scopes.
I will tell you this. Pulsar has the best customer service in the industry (personal and professional experience). Trijicon is good (personal experience). Flir is tough to deal with (personal experience and noted from people online). ATN has the worst reputation overall and reports range from excellent CS to long winded profanity laced descriptions of problems encountered. I have dealt with them twice that did not go well. Bering Optics is brand new to the thermal world and no word on their CS. N-Vision is a couple years into thermal and their CS is reported to be good as well.
ALL THERMAL COMPANIES HAVE PROBLEM UNITS SOMETIMES. That is just reality, I am afraid. So CS is important.
What is your budget?
What are you hunting?
What is the terrain of your 40 acres?
300 yards is your max range (I assume), so what would be your typical range and what would be your expected minimal range?
I will tell you that most people are not shooting 300 yards with thermal scopes on a regular basis and I think that mainly has to do with hunter skills, resolution issues, and environmental issues. I think my longest kill was a 360 yard shot that used a lot of Kentucky windage and elevation to drop a running hog. I prefer to keep my shots with ~240 yards, or about my far point blank range. Honestly, most hunters (particularly with thermal or night vision) don't usually hunt over 100 yards.
Seeing farther than 300 yards isn't a problem with most rifle scopes except the lowest end units. You can see that far, but you may only see blobs. Hunting with thermal is an exercise in learning to interpret blobs and silhouettes because the silhouette you see isn't always going to be a nice broadside like you see on a practice target of an animal. With time, you will learn to recognize animals by their size, shape, movement patterns. Making proper identifications is critical before you pull the trigger. In the right circumstances, deer can look like hogs, particularly a deer with its head down in higher grass. Calves can look like hogs. Deer and coyotes can be confused for one another. Coyotes and foxes can be confused for one another.
Here are a couple of my longer distance shots on coyotes in very good conditions.
255 Yards, open field, low grass, Trijicon IR Hunter MKIII 4.5x 60mm 640 resolution
245 Yards, open field, low grass, borrowed Pulsar Apex XQ50 3x 50mm 384 resolution