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As EB-1 says, your heavy kit stretches the series 1 even in the best of circumstances. Don't know about the new 6x legs, but Gitzo used to say that a 70-200/2.8 was the longest recommended lens on a 2-series, with 300/4 in a pinch. The 6x feel notably more stable so I would imagine that the 2-series would be fine with a 300/4.
You can probably wing it with a 1 series, but if it is the only tripod you plan on buying I would go with a 2 series. On the other hand, the 1 series is A LOT more compact for stuffing in a backpack or a carry-on.
Like many here, I have a 3-series for "around home base", and a 1-series for those times when I will need to lug things more than 3000 ft in the vertical direction.