The 54" John Deere hydraulic blade is really nice, and I assume you are asking about this. With the exception of different mounting brackets, it is basically the same blade used between the X series, 2210/2305 and the small framed 4000's (like yours). I have not had one in your application but did have one for my X 595. In that application, it did great. The plow was heavy enough to plow both snow and gravel/dirt, and it did a fine job. At 5-6 mph, one could plow pretty fast, and it was relatively easy to attach. One problem, I do not believe the blade was originally designed for the 4115. At least two posters noted that when angled, the blade was not as wide as the tractor!!! This is not good, especially for what is an over $1000 new purchase. I hesitate to say what to do, because only you know your situation, but if it were me, even though I liked the blade on mine, I think you might be disappointed, as your machine could easily handle a 72" blade. You might want to check out Curtis, American and other plow companies to see if you could get a wider one for less money.
John M