well, there is no need to worry about output... VESA is just a standard to display high-res screens, and many hybrid ones, like 320X400... It is just a "little driver" that allows games and apps to communicate with a standard way with the VGA...
as for linear framebuffer, if supported by the vga chipset, it uses some hidden features to speed the graphics output... it did made some difference, I remember running Genecyst, a MegaDrive emulator, and when I was using a linear framebuffer mode, I was getting 10-12 more fps.... it's nice
but again, 98% of dos games do not use these features...