I think the better question to ask your self, when debating whether to buy open or closed headphones, is what sonic quality do you value most and in what sort of environment will you be using them. If a more natural sound, larger soundstage, better imaging, and better bass is what you're after, then you should get the open ones. If you're looking for compromised sound, but better isolation, then the closed ones are for you. Personally, I own both an older pair of Grado SR-100's (open) and Westone UM-1's (in ear canal). I use each one quite a bit, depending on the circumstance. If I'm lying in bed next to my wife and she's trying to go to sleep, I use the Westone's. If I'm walking through the streets of a city with a lot of ambient noise, I use the Westone's. If I'm sitting on the couch in my family room, I use the Grado's. I prefer to use the Grado's whenever I can. However, given the situation, it isn't always practical to do so.
I'm not sure if this helps, but my recommendation would be to increase your budget a little and buy both an open and isolation type headphone. Something like the Grado SR-60 can be purchased for $69, while the Westone UM-1's can be had for ~$100. This way, you'll always have a quality headphone for all occasions. Or, if your budget is limited, I would pick up the Grado SR-60's right now for $69. Sonically, the SR-60's will destroy the HD-485's and will more than stack up to the HD-555's, at a lower pricepoint. Take that savings and, when you put some additional scratch together, buy a quality in-ear isolating headphone (like the Westone, Etyomic, Shure, etc.).