You should just go for a used RS-1 (or maybe HF-1/2) . It really does improve on everything in the lower models and since you'll end up there anyways it will be cheaper to just skip everything in between. Funny thing, I was trying out an HE-500 last week and my wife preferred the RS-1..
I hope to get an RS-1 someday. I still think though that the 225i is a good phone and is well worth every penny.