variable ND filter experiences.

Because you can compensate using the shutter. What is the deepest stop you find you must use to shoot in daylight (at 1/8000 or 1/4000 or whatever the top speed is)? Figure out the difference between that stop and f2.8 and buy an ND filter of that strength.

Chances are you won't need anything in between, especially if you're willing to boost your ISO to compensate, too. If not, you can get by with two ND filters.

For video you need a variable ND or set of NDs to maintain a constant shutter speed.

The Hoya NDs are very neutral and have great coatings, however they are not terribly durable in my experience:

http://www.bhphotovideo.com/c/search?Ntt=hoya+82mm+ND&N=0&InitialSearch=yes&sts=ma&Top+Nav-Search=

I have a $20 variable ND that sort of works but it is optically a mess. Big "X" over the frame at wide angles. Very soft toward the long end.