I did some more reading.
It appears the standard bootloader uses 2k of memory, and the optiboot uses 512 bytes (the readme claims it uses 1.5k less, hence I am assuming the standard bootloader uses 2k).
since I got a non R3 UNO, then the maximum sketch size I can upload is 30720 bytes right?
with ethernet+sd taking up about 26k of space, that leaves hardly any space left to do even just slightly complex routine.