The problem with most high-power NDs is the color cast--most of them are not a true warm cast, but rather have some magenta to them. This can be finicky to correct in post-processing if you are working in color. I suggest you take a long look at the Singh-Ray 10-Stop Mor-Slo if you are working in color, as this filter is specifically designed to overcome this deficiency. The Singh-Ray version also comes in both threaded and "square" formats. I prefer using Cokin-P as my base for such filters as that size works consistently for all but the biggest lenses while not taking up too much space (the Lee filter size is too large, expensive, and hard to find competing products for in my view). This is all my personal preferences, of course, and your mileage may vary. I can also vouch for the regular ND, grad, and polarizing filters from Singh-Ray--they're all top notch.