The closer the Vmps are the more efficient the system will be. As a general rule
if the Vmp's are within 0.5v of each other the loss will be slight.
It is helpful to calculate the actual working Vmp of the two panels. The specifications list the Vmp at 25 deg C which is very unrealistic. You can use the temperature coefficients to calculate the Vmp at a more appropiate panel temperature. It is even possible to, roughly calculate the worst case loss. With the full I/V curve it can even be calculated accuratly, but the rough worst case numbers will give you some idea.
If you list all
the specs (the temperature coefficients are needed) for the two panels I can do the rough version.
Other than the (slight) loss in power the voltage mismatch will not cause any other problems. Occasionally controllers can get temporarily stuck tracking the wrong Vmp, but this is more likely to happen with shadows than a Vmp mismatch. Good controllers like the Outback are much less likely to do this.