Each time i want  to use framebuffer in console i have to search kernel doc about vesafb about possible vga= entries.

Here they are :

{.alt2 style="border: 1px inset ; margin: 0px; padding: 6px; overflow: auto; width: 640px; height: 114px"} | 640x480 800x600 1024x768 1280x1024 ----+------------------------------------- 256 | 0x301 0x303 0x305 0x307 32k | 0x310 0x313 0x316 0x319 64k | 0x311 0x314 0x317 0x31A 16M | 0x312 0x315 0x318 0x31B

You can use it like that or convert hex in decimal : 0x317 then becomes 791