If you have a decent guitar with good pickups and you use a thicker guage of strings (for a step down 10s would be fine but 11s would work as well) then I don't think it'll be major. You'll want to make sure that the intonation is adjusted, though. An amp with a good bottom end wouldn't hurt, either. Another thing to consider is the scale length of the neck. A 25.5 inch neck will handle a step down EASILY but if you want to get another step lower then I would suggest a
baritone guitar.
But really, I can't stress enough how important having good pickups and especially have a good amp is going to affect this. I've found that a lot of stock pickups (especially cheap ones) sound like crap when you downtune a guitar because they're really only designed to handle standard tuning. Quality pickups like Dimarzios and EMGs can help to rectify this problem.
