I went from a 50" to the 47" and honestly it didn't bother me at all mate, it's worth the sacrifice for the passive glasses trust me. Visually, hmmm that's a tough one, I'm not using the best material, all the material I've got has been 720p to start with so when I say it's looked softer than active then perhaps it was a bit unfair as I haven't been feeding it the best resolution anyway. From what I've seen the passive sets are more than capable of a cracking 3D image and avatar that I watched today on the LD920 I've currently got looked superb. Honestly yes I think there is a difference but I'm beginning to realise it's worth it for the benefits of passive glasses, no flicker, no sore eyes, no headache, cheap as chips to buy/replace etc

What I will say is that I think you'd need to be sat quite far away from the 55" to prevent seeing the lines and loss of resolution. I'm just over 2m away from the 47" and it's ok but I suspect if it was 55" I'd want to be sat at least another half a metre further back, just something to bear in mind