I've seen claims that the newer 2-series Gitzos have capacity similar to the older 3-series. I've used a Gitzo 1325 with excellent results to mount my Canon 300/2.8 IS lens for several years. I'm attracted by the faster setup time on the new 6x Gitzo tripods, and the lighter weight of the Gitzo 2530 appeals, especially since I'm doing more landscape photography and hiking more now. The rated load on the 2530 is minisculely less than the load for the 1325, which seems just fine for my 300/2.8--The 1325 is more than I actually need there. I know people who are satisfied using a current 2-series, such as the 1228 with a 300/2.8. And since a 3-series is adequate for a 500 or perhaps even a 600mm lens, and the 2530 has almost the same capacity, it seems reasonable that the 2530 could handle a 300/2.8 lens (I'm NOT suggesting it be used for a 500 or 600mm lens). But when I look at the Gitzo promotional literature, found on the Bogen Imaging website, I see that the 2530 is recommended for lenses no longer than 200mm! Since I'd like to use my 300/2.8, and probably use teleconverters on the lens, that bothers me about the soundness of my thinking. I'd use the new tripod with a RRS BH-55 ballhead much of the time, but replace that with a Kirk BH-3 when I left the 300/2.8 at home and was hiking with lighter lenses. After the 300/2.8, my next largest lens is quite a step down in weight, a 100-400L. I don't own any larger lenses than the 300/2.8, and doubt very much that I ever will. Camera used with these is a (original version) 1Ds. When and if a Canon 5D replacement comes out, I will purchase one if it looks good at the time. I'd probably keep the Gitzo 1325 around for shooting near the car (the extra few inches of height over the 2530 will be an advantage). Am I misinterpreting the Gitzo literature on the 2530's capacity? Anyone with experience with the Gitzo 2530 or Gitzo 2540 and larger lenses, especially the 300/2.8?
My only concern is the pod will hold the weight but you may get some shake. For example when the wind kicks up a bit. The 300 is a big lens!
I have a 2540 and use it with my D200. I use a RRS BH-40 and the biggest lens I have is the 70-200 VR. This, along with the MB-D200 and the occasional teleconverter, is probably about 4 lbs. lighter than your setup. While I love this tripod for its carry weight and ease of use, I am a little disappointed with its sturdiness. You might have a hard time with that 300mm/f2.8.
Weight is not the critical issue here, it's torsion. According to Gitzo's 2007 catalog, higher series tripods offer more torsional rigidity and consequently have a lower torsion angle. Series 3 tripod is recommended for 300mm lens. If you decide to use a 300mm lens on a Series 2 tripod, you?ll need to pay more attention to keeping your equipment steady and may have to avoid critical conditions like strong winds. I hike a lot too, but I don't bring any heavy artillery with me on long hikes. I use a series 2 tripod, a Really Right Stuff BL25 head, and my Leica M. I also have a 1325 tripod for my 300/2.8 tele and medium format camera.
From the comments I've read from those who have upgrade from the older 13xx carbon fiber tripods to the GT35xx tripods, they are definitely nicer, though not dramatically more stable. Since the GT2530 is really just an upgraded 1257, it would probably remain marginal for use with a 300mm f/2.8. I'd suggest trading in your 1325 for a GT3530LVS (the video model is the only way to get the same size/dimensions as the 1325). You'd save a 1/2 lb, get the anti-twist legs and have a higher weight rating. Then you wouldn't need to worry about shooting your 300mm in windy conditions. If you are trying to lighten your current tripod to make it more condusive to carrying, you might look at the Markins M20 as a replacement ballhead for both the BH-3 and RRS BH-55. Its a very good head, much sturdier than the BH-3 despite weighing only 1 oz more, capable of handling a 300mm f/2.8, and 1/2 lb lighter than the BH-55. The BH-55 is a very good head, though. I might just be willing to carry the extra 1/2 lb and use the BH-55.