It's kind of funny that here in So Cal we have some high level repeaters (5000'+ elevation) that you can hit from 40 miles out with an HT no problem. No problem if they're not busy that is... There are a couple of them that are SO busy (and so loaded with jammers) that you'll get crushed using 50w on an omni with line of sight at 10 miles out, and "using the minimum amount of power to make the contact" isn't in the cards. Brutal...
Full duplex operation, cavity filters, etc... are a must, just to hear if your signal is getting in. One of the better signals on one that we used to use all the time came from 30 miles away by the operator that I mentioned in my post above. He was running a Cushcraft 26B2 (co-phased 13B2's) on 200w, but kicked in a 600w Henry when he needed to. When he switched to a pair of M2 2M12's, I don't think he ever turned the Henry on again. The M2 beams made a significant difference. M2 seems to be more "honest" in their gain ratings...
Many of us use modeling software before making changes to our stations. The "Radio Mobile" site (
Radio Mobile Online) offers coverage maps that allow you to plug in variables such as watts out, antenna gain & height, etc... It gives you a visual of what your signal will do as far as coverage by simple plugging in the numbers. It would be worth creating a (free) account and plugging in some numbers while shopping for antennas.
"Field Strength & Power Estimator" is a free smart phone app that I've used quite a bit in an effort to "compete".
By plotting distances in Google Earth, you can plug in numbers and see how much of your signal is actually making it to the receive antenna. This software assumes that you've got line of site between the antennas, so there is no input field for antenna height. However, seeing how much of your signal is actually making it to the receive antenna is quite interesting by changing antenna gain factors, watts out, etc...