so ive been running a Diamond X300 for a few years now and honestly its been fine but i keep reading that stepping up to a longer collinear makes a noticeable difference on 2m especially for hitting repeaters that are kind of on the edge. the two that keep coming up are the Comet GP-6 and the Diamond X510 and i cant find anyone whos actually done a direct comparison, most of the threads i find are from like 2014 and half the links are dead.

my situation is im on a flat lot, single story house, antenna is on a chimney mount maybe 20 feet up total. nearest repeater thats giving me trouble is about 35 miles out with some terrain in the way, not a huge hill but enough to be annoying. i know a collinear isnt going to punch through a mountain but wondering if the extra gain is worth the upgrade or if im just chasing numbers at this point.

also the GP-6 is quite a bit longer — does that become a real wind loading issue or are people generally fine with it on a standard chimney mount? im in the midwest so we do get some weather.

ran an X510 for about 3 years before switching to a GP-6 and honestly the difference on 2m was noticeable but not dramatic, maybe a couple db real world which is still a full S unit so not nothing. the bigger thing i noticed was 70cm performance — the X510 always felt a little soft up there to me and the GP-6 seemed punchier, though i never actually measured it so take that for what its worth.

wind loading on the GP-6 is real, thats not just spec sheet stuff. i had mine on a pushup mast and after one bad windstorm the whole thing was canted about 15 degrees. moved it to a proper 1.5 inch pipe mount with a decent base and its been solid since. for a chimney mount id make sure your straps are in good shape and maybe add a third one if you only have two. midwest wind can get sketchy and that antenna is basically a sail once you get above maybe 20 mph sustained.

if youre 35 miles out with terrain honestly you might get more bang for your buck pointing a small yagi at that specific repeater instead of trying to squeeze it out of a collinear, but i get it if you want something omnidirectional for everyday use.

dont have the X510 but ive had the GP-6 up for about a year and a half, no complaints so far. my mount is just a j-pipe off the eave not a chimney mount so cant speak to that specifically. the antenna itself feels well built, connectors are solid, no issues with the SO-239 at the base getting wet or anything like that.

one thing nobody mentions is how annoying it is to get that thing in the attic or up a staircase when you first buy it, its just long and awkward lol. small thing but yeah.