That's a very nice tripod, but as you say the head is not so good. Your choice really depends on your camera equipment, especially the lenses. I've used Markins Q3T heads for nearly four years, first on a Gitzo 1541T and currently on a Benro C2680T. They are good - no question, and with a max diameter of 50mm will allow the legs of your 2580 to fold back parallel to the center column. An alternative is difficult to talk about as no other company has achieved the feat of housing a 38mm ball in a head with a 50mm max diameter. It's a brilliant piece of engineering.
There are drawbacks though. You see frequent reports of locked balls because users don't understand how to use the friction (drag) properly. It doesn't help that the instructions that come with the product are a bit skimpy. Many users also seem frustrated with the way that the panning knob works; they're expecting it to lock the housing rotation but it is actually a brake by design and not a lock. I have never had either of these issues but plenty others have.
I've had two problems with mine: When using a Nikkor 17-55/2.8 on a Fuji S5 body the ballhead binds at angles around 25-30° from the horizontal. I've owned three Q3T ballheads and they have all done this. So if you use a lens with a particularly large lump of glass at the end I'd urge caution WRT this ballhead. Second, it locks up in cold weather. We've recently had some fairly cold weather here: 1°F (-17°C) and the ballhead got cold and was locked solid. After it warmed up a bit it was binding and I took it off the tripod and replaced it with another. Later I cleaned and polished the ball and it was fine.
I've now replaced my Q3T with a different brand that's a larger head as I don't need to fold back my traveler's legs. I lived in Utrecht for a while so I know it can get cold in the winter in Holland. If you have heavy glass and/or it gets seriously cold where you live I would not recommend the Q3T. In every other situation I've experienced though it has been perfect and I still think it's out on its own in its class. The one alternative that I think you might consider is the RRS BH-40. It has a ball diameter of 40mm and a base diameter of 53mm and it might fit on a 2-series Gitzo traveler. From reports it doesn't lock up in freezing weather.