Volume should be ok. I have a Riff Raff neck paired with the Painkiller bridge, so there is no problem there.
The hotness will affect the gain of the pair obviously, so if you want that to be level go for similar pups.
EQ doesn't have to be similar, as rules are made to be broken, it is your sound after all. However, some pups vary quite a bit in the EQ department more than others, so a carelss match might make you unhappy, which we don't want. :)