I've got the
B+W 10-stop but Im now getting rid of it since it gives a very strong magenta/red colour cast that is hard to remove in post processing. Im getting the lee 10 stop hoping it wont give any colour cast, I already have the lee 0.9 ND which is great peice of glass

. Hope this helps a little in making a decision on the best brand.
The B+W is a little warm in colour. I've compared it to the Lee Big Stopper and that is fractionally bluish (hardly noticeable). Lee admit to this, but it is less blue than the B+W is orange. If accurate colour is essential, you will need to do a custom white balance with either of them. Maybe you have a poor sample of the B+W - they do vary in density slightly, so maybe in colour also?
The most neutral dark ND I've tried is the Light Craft Fader. They have an improved MkII version coming any day now, which I have on order, and that looks very promising. They also do a 9-stops X500 multicoated in 77mm only (which I haven't tried) but that is also out of stock ATM (from Premier Ink
http://www.premier-ink.co.uk/advanc...ription=1&keywords=light+craft+77mm&x=48&y=10 ). Hoya make a 9-stops X400 which is special order only, is coated, a bit expensive and also a bit warm so I've heard.
For anybody that already has a Lee filter system, I think the Big Stopper is the best bet. It a good filter and I like the way it slips in with that neat gasket, or clips on with the mount.
On the covering the viewfinder eyepiece thing, yes definitely do it always. On the three cameras I've tried, my Canon 350D got a grey fog through the eyepiece, 40D produced a rather attractive rainbow/sunset look in the top of the frame

while my 5D2 seems to be pretty well sealed, but I'm taking no chances - that's what the eyepiece cover is for after all.