Monitor resolution

[tohei1234]

I have installed two Guests same Windows7, hopefully all parameters inside the configurations are the same. (I think so)
I have two Monitors. But the max. resolutions at the two monitors I can choose are different.
First guest: MonitorA: 2560x1309 (max.) MonitorB: 1600x1200 (max.)
Second guest: MonitorA: 2549x1268 (max.) MonitorB: 2549x1268 (max.) that I would prefer for the first guest too.
I use VirtulaBox Vers. 5.0.20r106931 on an iMac27" with 32GB memory as host.