I can't speak about those two cards exactly and their differences but it you look at the two cards you mentioned here - Nvidia Quadro - Wikipedia - there is quite a big jump up in specs from one card to another.
It may be worth noting that component count isn't always the best comparison of models as those parts could be simple or very complex with a lot of mates/relations/references/etc.
The P4000 is a pretty high end card in my opinion which personally I think should be more than enough for most people with a few even higher performance (and dearer) cards if required.
I have made due with a K2000, but still had to be very aware of large assembly challenges.
I have always had good performance with M4000, but the P4000 gives you more headroom on performance.
Video cards is the last place I cut the budget. But on the same hand I tend to purchase used Quadros and have had good results.