Don't know about Europe but here in USA, Captain (PIC) time is ABSOLUTELY ESSENTIAL in getting hired onto bigger/better gigs.
Turning down an E145 CA slot for more SIC time (even in an Airbus) would be considered a lateral, or even downward, move here.
I would say stick with the CA upgrade, but then again I'm not sure if Europe has the same adherence to PIC time when looking to move on.