The NMO really is the best option. Just be sure and get a good brand antenna and NMO mount. I've found some of the imported (Comet and Diamond) antennas have a slightly different thread than the original Motorola NMO spec.
As for distance, 75 watts won't get you much more range than 15 watts on simplex for 2m/70cm. VHF/UHF (esp FM) is basically line of sight. I've been able to get 5-6 miles on occasion, unless someone was at a higher elevation. On water, your distances will significantly increase. Now with repeaters, you might benefit by having more wattage. I've been able to regularly hit some repeaters 50-100 miles away with 15-45 watts. It all depends on the repeater elevation and whether buildings or mountains are obstructing your signal.
In the end, if your looking for long range communications, you'll have to go HF so you can benefit from groundwave or ionospheric bounce (skip). On 10m (28mHz), you'll typically see 10-30 miles on ground wave. On the lower bands, you may be able to talk significantly farther, even without ionospheric propagation.
N4WFB
if you can hit a repeater at 50-100 miles, couldnt you in theory do that simplex with another rig that was set up similar to yours? if they can hear you, you should be able to hear them, right?
say they had a jpole on the house, and i did too at 30-50 miles that should be doable if elevations are agreeable, no?
and yes i think 10m would be best, but really the 2m would be SHTF comm for the family, and extended family. we are mostly across north atlanta so i think 2m would be okay. i need to test it all out. i dont even have my callsign yet. haha.