You are about to add $250 to the cost of the tripod that will actually serve your needs and not vibrate and spoil your shots. I am going to take a wild guess and say that you are using a crop sensor camera - how do you expect this tripod to hold a lens with a 900mm (or 960 if Canon) steady with that tripod?

I think you need to do more research.

You can start here:

http://bythom.com/support.htm

Then you definitely need to read this:

http://blog.reallyrightstuff.com/choosing-a-tripod-part-1/
http://blog.reallyrightstuff.com/choosing-a-tripod-part-2/
http://blog.reallyrightstuff.com/choosing-a-tripod-part-3/

And the Gitzo tripod catalog - which you can download Here

Eventually you'll come to several realizations:

1. That when a manufacturer sells a tripod like this - http://www.reallyrightstuff.com/TQC-14-Quick-column-series-1-tripod for $900 and only recommends it for use with 200-300mm lenses, there is no way that your $250 tripod is going to be stable with a 900mm lens - ever.

2. That for any lens longer than 600mm you will need a very substantial tripod, equivalent to a Gitzo Series 5 or RRS Series 4. These start at around $1000 and go up from there. And you still need to add a head, which can be as modest as a Manfrotto 393 for $!90 (I have used this for 10 yrs with a 600mmF4 with zero issues at all), or if you need locking, a Wimberley, or Wimberley knock off - which start at around $250 and go up to over $1000.

3. That the Sigma lens has excellent stabilization, and if you decide to hand hold it, you will be able to shoot down to 1/25 sec at maximum magnification, and still get sharp images. (See attached) And you may not actually need to throw away $250 on a piece of equipment which only has value to some company's sales and marketing group, and could actually result in damaged equipment when (not if) it fails.

4. That a $250 tripod is the equivalent of buying an Eastern Block Yugo vehicle, when what you really need is a car.

Putting a camera with a Sigma 150-600 reminds me of the last attached image - just because you can doesn't mean you should.

Ok, I am being very sarcastic and using this opportunity to have a little fun at your expense. But seriously, don't waste your money. You don't need to buy a $1000 or higher tripod. But you should be looking for a tripod with a top tube diameter no less than 37mm (like my Feisol CT3472, or a CT3372 - $500 without the rapid leg lock option) if you expect to get decent results. Less than that and your percentage of keepers goes down.

I have done some research and am purchasing a Vanguard 263 tripod. My question is this... Do I go with the pistol grip or the standard head? The pricing is not much different and IF the pistol grip adds more versatility and ease, I will go that direction. I am interested in mostly landscape and nature photography and will also purchase a gimbal head for a Sigma 150-600 lens. Also, should I spend the extra money on the carbon fiber or go with the aluminum frame? I will sometimes be lugging my gear for a few miles to get to the shot.

I have done some research and am purchasing a Vanguard 263 tripod. My question is this... Do I go with the pistol grip or the standard head? The pricing is not much different and IF the pistol grip adds more versatility and ease, I will go that direction. I am interested in mostly landscape and nature photography and will also purchase a gimbal head for a Sigma 150-600 lens. Also, should I spend the extra money on the carbon fiber or go with the aluminum frame? I will sometimes be lugging my gear for a few miles to get to the shot.