SED1520 is a graphic display and would if supported be handled from u8g lib build in. This already uses spi e.g. for ST920 display and KS0108 with parallel connection is also included (not sur eif I have seen spi version).
Hardware SPI is normally used for SD Card and on display pins no hardware spi pin is available at the right spot (e.g. reprapdiscount display) so it uses software spi. So what is faster is hard to say. SPI in general is fast but if you use the fast hardware spi you might get problems with sd card. But main reason is I have no sold display that uses spi so I never wrote a driver for it. As you see you could easily add a additional driver like i2c->4bit parallel and add it. SO if you have a working implementation for work092 make a push request and I can update it for all.
