I was interested in this too, but after reading (below) from the FreeBSD handbook, I thought I'd wait a while before I bomb my system. I hope someone knows an easier way...
3.2.6 Changing Console Video Modes
The FreeBSD console default video mode may be adjusted to 1024x768, 1280x1024, or any other size supported by your graphics chip and monitor. To use a different video mode, you first must recompile your kernel and include two additional options:
Once the kernel has been recompiled with these two options, you can then determine what video modes are supported by your hardware by using the vidcontrol(1) utility. To get a list of supported video modes issue the following:
# vidcontrol -i mode
The output of this command is a list of video modes that are supported by your hardware. You can then choose to use a new video mode by passing it to vidcontrol(1) in a root console:
# vidcontrol MODE_279
If the new video mode is acceptable, it can be permanently set on boot by setting it in the /etc/rc.conf file: