Best sports lens for D5100? 300mm Equestrian Photography?

What's the best lens for sports photography (Equestrian photography) for the Nikon D5100? I'm thinking of getting one… Needs to (obviously) have a fast, quiet, AF and no more than $400. I'm used to usong a 300mm on my Sony alpha so I think a 300 should work BUT if 200 is really recommended, I'll live. Thanks!

Added (1). Oh and also it needs to be RAZOR sharp. I want DETAIL.

The best lens in the 300mm range would be the 300mm f2.8 VR. After that either the 70-200 f2.8 or the 200-400 f4. All three of these are well beyond your pricerange.

I think your best bet would be to start searching for a refurbished or used 70-300 VR. Even though it's not stellar after 260mm it's the best lens in your budget.

Nikon 55-250mm, 55-300mm, 70-300mm.

Razor sharp? That depends on your settings. You want details? I think you should read a bit more about these cameras, most of the stuff depends on you.

Here's a Lens Buying Guide - http://www.the-dslr-photographer.com/2009/11/buying-a-lens/

What you want is available, just not for $400.

With your budget, you are going to have to compromise something. You would be looking at the Nikon 55-300 or 70-300 ED (if you can find one) for under $400. Don't bother with the 70-300 G model. There are no 70-200 lenses in your price range. The least expensive is $700 for the Tamron 70-200 f/2.8 model.

You need to decide if you can work with one of these lenses in your price range, or if you need to keep saving until you can afford something better.

The latest version of the venerable Tamron 90mm Macro, this lens is widely used by naturalists and other pros who need top imaging performance plus a longer lens-to-subject (working) distance to enable easier lighting and access to skittish subjects. Improved resolution, chromatic correction, and coatings make it a superb choice for full-frame or APS-C format SLRs. Tamron introduces a new version of the famous 90mm macro lens for film and digital photography. Tamron's 90mm macro lens, often referred to as "the portrait macro" and loved by photographers all over the world, is now reborn as a Di lens that is perfect for use with both film and digital cameras.