For the record there are very few differences between a crossbow and a regular compound bow regardless of what you may here from others. The main differences are in the fact that when shooting a regular bow you would a much longer draw length, so let's say for example purposes that your draw length is 28". This means that when you release an arrow you would have approximately that number of inches (minus your bows brace height) to develop the 300 + fps of arrow velocity required to hit and penetrate your target.
"Penetration" is a formula based on mass weight x speed, so it's the weight of your arrow and point x the fps you've generated coming off your bow.
On a crossbow, which is nothing more that a bow turned sideways, mounted to a stock and operated off a trigger rather than a string release, you only have approximately 13" of cable travel in which to develop the same or greater velocity as you do on your compound bow at almost 28" of string travel. This means that it would require much more bow poundage to achieve the same or greater arrow velocities in that short of a distance with the crossbow because the bow is much shorter and the string travel is greatly reduced. The mass weight of the arrow is also much lighter, due to the fact that the arrow shaft has been shortened by several inches.
There is no difference in performance between a cheap or medium priced crossbow that shoots an arrow at 350 fps and an expensive one. The expensive ones may have more amenities on them or may be more well built or even have better sight systems, but 350 fps is 350 fps no matter what it comes out of, so the accuracy and performance of a 350 fps projectile remains the same as long as the mass weight remains the same.
The better high performance crossbows that you refer to usually have velocities far exceeding 350 fps and are generally in the range of 400 + fps. This may not sound like much, but every 25 fps of an increase is very significant. In order to achieve any type of useable accuracy at anything over 50 yards you would need a crossbow that shoots minimally 375 fps, but 400 + fps will allow accuracy to at least 100 yards with enough penetration to pass through a large animal.
If you look at the design of the PSE TAC15
/ 15i crossbows, they are the only crossbows to shoot a 22.25" arrow. This means that they have a significantly longer cable stroke than any other production made crossbow. Their bow weight is 155 lbs. and the velocity is an average of 405 fps. Since the cable is cranked back into the load position by a cranking mechanism, it requires very little strength or effort to turn the handle to load these units.
This makes it a great shooting crossbow with extreme accuracy, but that doesn't necessarily mean it's a great hunting crossbow. Power and accuracy are two important factors, but size and weight are also important for many hunters.
The TAC Series crossbows are a bit long and can be heavy compared to many of the less expensive crossbows on the market. For those looking for light and short, this is not going to be a good match up. For those looking for extreme accuracy at all distances up to and exceeding 100 yards, this is the best xbow available.
There are no crossbows that even come close to covering all the bases in all of these areas. Pick and choose those qualities that are most important to you and then invest on that basis. Today's latest generation of crossbows are making enormous advances in performance and durability with the new technology and the latest new materials and composites available, but the same can be said about today's new generations of compound bows. As we know these materials heavily impact the price to performance ratio.
The biggest difference is that even attempting to shoot a compound bow at targets 100 yards or more is almost unheard of, but with the right crossbow and a good deal of tuning work, it's very doable for the average person with the right crossbow.
Hope this helps with the basics!