According to Wildi in the fifth edition of The Hasselblad Manual, “Compared to the original Acute-Matte, the D-type screen is slightly more diffusing for stable exposure metering and the out-of-focus portions of the image are more blurred… the difference is small…”
I had to look this up because, even though I have used both types of screens, I have never noticed any difference.
The price difference does concern me. If both camera kits are in equal condition, the 503CW should be priced higher. The fact that the 501CM is considerably higher would indicate that it is in much better condition. Examine all the photos very carefully and try and spot any differences, and check the serial numbers for the dates of manufacture.
Strictly on the basis of what you have presented, I would get the 501CM.