I have a Hartke 3500 and the 2.5xl and 115xl cabs and I like them a lot.
But
I have nothing to compare them to as I have only been playing for a year and it's the first and only rig I've ever had. I chose it because, having researched the subject to death, it seemed to be the rig to go for in the price range. Eden, Ampeg etc would be nice but I'll wait until "I'm good enough to justify it"
Sure Jaco used Hartke gear, but that was 1986 or something and a large bucket with a pfeizoelectric balloon inside it was still considered pretty neat back then. However, I see that Jack Bruce uses Hartke and I've seen others use it too.
I don't gig (I'm a classical pianist) but my circumstances are such that I can play as loud as I like - occasionaly my curiosity gets the better of me ... I find that anything above 7 is just too distorted when you're standing near this thing (but sounds nice about 100yds away LOL). When sitting noodling in my house and practicing my arpeggios about 1.5 is ample.
The 2.5 sounds fine on it's own as does the 115, although I think there is a nicer low end with the 115. But this could have a lot to do with the room I have them in, I don't know enough about it. I see many folks in the know say that the 115xl is unnecessary and just to go with the 4.5 or even 2 of them, I've seen enough gigs with such a rig to believe this and I guess these folks know far more than this newbie. Hang fire on the 115xl?
Good luck and enjoy
BH