I've owned all of the 410 cabs mentioned here. The GS410 has a sonic profile similar to the Eden 410xlt. It will cut thru a mix like a saw. It's a LOUD and punchy cab. The berg AE410 is has more depth and the Epifani has more bottom.
Although I think both the berg and epi are full sounding cabs, to my ears the aggie cuts thru a more in the mix.That being said, it's not the smoothest cabinet in the world, but it has great growl and can work in most situations.
i too always thought the gs410 was like the smarter, more articulate, less aggressive and more versatile bro of the 410xlt. similar vibe, but the aguilar cab is just more pleasant to listen to.
but yea, when you read stuff on the internets and listen to people who talk adamantly about their opinions on something that you may and may not exactly share said opinions, bad things can happen.
course, with that said and not to steer you closer to futility

, the gs410 takes to EQ'ing much better, and either aguilar amp sound monster thru it. have you tried tweaking the lower mids and lows knob on the ag500?
btw, while my memory's a little fuzzy, i do remember doing a massive shootout at bass specialties w/ the 750 into an hs410, gs410, ae410, and a sadowsky sa410.
in the end, i thought the ae410 was the worst match for the 750. the lows seemed rather pillowy and diffuse, and just isnt nearly as authoratative as the other cabs. the hs410 was great with its steely pounding lower end, but the word "fat" didnt really enter my mind. but the sadowsky cab was IT. fat lower mids w/ that pounding, steely low end, and a nice airy top end. just a terrific mix! and i didnt have to mess w/ the 750's eq all that much. heck, i'm still looking for a cheaper 750 to go along w/ my sa410 cab. and whatdya know, i love my ag500 w/ the sa410, too.