Hi Joseph,
I have the 3940J with the roman numbers, bought it some time ago (1999 I think). Compared with the "classic" dial it is a bit brighter as the dial is white compared to silverish/creamish. The roman dial is quite rare but I would say only due to that fact that there is much less demand. Would say there were up to 1000 pieces made with roman dials (in yellow, white and rose metal combined) and 5000 to 10000 with the classic dial (but these numbers are pure speculation.
Best regards