well I went to the local Audio/video store and listened to the Grado 225 and the B&W P5, here are my comments
I used my iPod Touch with my P51 RSA amp
P5
I listened to these first and the sound was quite good, the isolation was better than expected with these non-canceling phones. I listened to some rock, classical, some guitar and was very happy with them. I did notice that it seemed to be missing some of the frequency range I expected. I am not sure why, maybe because they are brand new and need to be broken in?
SR225i
I listened to these next and it was very evident that these are open phones, the ambient noise was very transparent Through the left and right. The sound seemed a little cleaner, crisper and the base tighter. These phones have what I expect for this price
so for me, even thought these are open phones and semi-portable, ie the plane, home, office. I am leaning towards the SR225i
So, in summary I suggest what ever phone you are looking at is that you bring your own music and do a test drive yourself, you will find you will not be disappointed!!!!