I made the jump from 530 to 1040 mainly because 540 was not available at the time last year, and the 530 battery capacity was reduced. Also, the screen of 530 had taken some beating.
I am happy with the 1040 but for MTB it could be a bit smaller. I still keep 530 for commuting. Atleast i save few seconds here and there to swap the computers.
The 1040 usability with touch screen is much improved vs 530 buttons. Also everything works much faster.