What is the speed of your scope? You will need a very fast scope to get reasonable acquisition times with say a 3nm Ha filter in place, otherwise your exposure times will actually be astronomical.
You would want at least a 7nm Ha filter, spring for a 3nm if you can afford it.
Here are some examples with a QHY8 with and without using a 7nm Ha filter
With:
http://bp1.blogger.com/_9HcYqbvUc4s/...1600-h/M82.jpg
Without:
http://bp2.blogger.com/_9HcYqbvUc4s/...lor+scaled.jpg
Be aware that your subs times can get up over 20 minutes with the filter on, your mount and guiding has to be up to it otherwise you may be wasting your money. You need to go 2" which adds to the cost.