Why the PSP?
If we remove playstation console only 4 consoles/handheld outsold PSP and we know wii and ds sold that much because of casuals and those one won't buy another consoles.
I think it's not difficult to sell more then NES which sold 60m but it's more difficult to sell more then PSP
PS4 - over 100 millions let's say 120m
Xbox One - 70m
Wii U - 25m
Vita - 15m if it will not get Final Fantasy Kingdoms Heart and Monster Hunter 20m otherwise
3DS - 80m