Just set the thumbnail size in the gallery plugin to be the larger size that you need.
Then if you need the gallery image to show in vcard as well, but smaller, then use CSS to do so.
Just remember, when you set a different thumbnail size for the gallery image, you will need to upload an image again to get it to resize to the larger settings you just changed. What I mean is, the gallery thumbnail creation occurs when a new image is uploaded based on the settings at that time.