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That's the tripod I use and I highly recommend it. I'd sooner toss my 24-70 over a cliff than leave it behind. Think of it this way - if you're missing shots with the 300 due to inadequate support, then that lens is useless and a waste of money - at least until it has proper support.
I use my 3 series as my "normal" tripod too. It's super with every lens on up to the 300 2.8 (although, that one usually lands on my 5 series). I could go with a smaller, slightly lighter setup, but once you use a good sturdy tripod like that, you won't go back to anything else.
Besides, not sure what other lenses you have, but a cheap set of extension tubes might be a good stop-gap for macros. There is no good substitute for a good tripod.
PS - A tripod like that may very well outlast a lens too - for many it's a once-in-a-lifetime investment. (I'm hard on my stuff, but I still expect to get a good 10-15 years from mine)