I would go with a 5' blade on a BX. A 4' is not wide enough cut your tracks when you angle the blade and a 6' would be too much. Ray @ Woodstock Equipment has a Land Pride Rb0560 that was Kubota orange for $450. I am not a big fan of the TSC blades. I guess it would be so so on a BX but there are better blades out there. I just sold a blade this week I had for the BX and bought a new to me blade. Here is the link to my thread.
I would stick wih a 5' blade as it will shove you around with a full blade of dirt or wet snow. Look on CL and in this instance a light weight blade will fill the bill. Used $150 or so depending on brand and condition.
I saw your thread Roger, that's why I started this one. Again cost is my main hurdle. Do they go bad or reach a point they don't work anymore? Just want this one mainly for very light work. After I know what I'm doing maybe I'll upgrade.