Aside from depth, you'll also want to consider current. I've fished intermediate lines in 12 feet of water and 350 grain sinkers in 5 ft with heavy currents. With your 8wt you could use a 300 grain sinking line if needed. This will allow you to quickly get down and stay there even when making fast strips. A floating line might allow the fly to sink but when it swings in a current and is retrieved, it will pull the fly back to the surface. Of course if your in 2-4' of water then that's perfectly fine. If you just need a starting point, and the water is over 4 or 5' then I would go with the intermediate. You can retrieve it quickly and stay up in the top three or four feet or let it sink into the deeper slow pools. Whatever you do, just make sure you get down to where the fish are!
Bill O.
www.oysterbamboo.com