I am not sure what you mean by this. Which 2 bytes? Just the number itself in binary (MSB then LSB)?
Receiving 2 bytes will always be faster than receiving 4 bytes [e.g."512\n"] but you then have the issue of figuring out if you get out of sync and start receiving LSB then MSB which means you need some sort of marker again and since you are receiving binary, you could theoretically receive any value 0x00 - 0xFF so there is no safe marker to use.
IF speed is really an issue, you can always bump your baud rate to 115200 or higher