Two images using nd1000 nd filter to show water movement. 3.2 seconds and 8 seconds . most of the 8 second images were quite sharp , even with a slight breeze.
But adjusting iso made No difference to either screen brightness or the Histogram, which makes judging exposure very difficult. will need to check each image in the library after taking to check exposure!
I'm yet to do any daytime long exposures with the NDs, but I'm astounded that you're getting 8 second stable exposures. I wouldn't have even considered going beyond my maximum 2" but I'll be pushing my exposures a little more from now on.