As far as the FPV, you are not alone. I've been trying to fly through wooded trails. Originally I was hoping for a 1000 yard range, and have since dropped that to about 400 yards and will probably have to drop my expectations even lower. I've tried several transmittors/cameras, 2 receivers and several antennas and so far the best antenna has been the helical and an omnidirectional with a diversity receiver. I also mounted it on a tripod with about a ten foot pole and I got a slight improvement with a as well. I don't know if 5.8ghz improves with height (still learning) but it could have something to do with ground reflection and it did seem to improve. There is a Cellular wireless skew- planer omnidirectional that's supposed to be pretty good, but I have not gotten to it yet. I have an Aomway omni directional that I intend on testing (if it ever stops raining), but Ive found so far that you pay a lot of money to experiment with minimal improvement when using 5.8ghz. I recently bought a 900mhz system to try, but the video is crappy and antenna options are limited because the antenna needs to be very large when tuned to 900mhz. more tuning and possibly a low pass filter or some other tweak will be needed to find the full potential of the 900Mhz system. So far I wasn't impressed with it and have since moved on to more quad builds for the time being but will get back to it as some point.
I think I understand what you want (I've seen the videos of guys flying awesome wooded trails) and I'm still wondering how people get the quality and range to fly those challenging and very wooded paths. Seems like there are only a few possiblities- 1) they have found the magic bullet combo that allows for such awesome flying. they have a ton of time and money into it and are not just going to give up the information. 2) They are exceptional pilots and can somehow fly through all the static and drop outs associated with 5.8ghz in highly wooded areas, at long range. 3) The idea has crossed my mind that they are 'doctored' videos that have been edited to appear as some long range highly forested adventure, that looks really cool but is not reality.
ETA- a 4th option is that they are not using 5.8ghz. If you are in the us you are limited to 910mhz, 2.4 ghz and 5.8ghz. Anything else you need a HAM operators license. Which I may get at some point to continue experimenting.