in dual mode you get 2 bits for every spi clk pulse one bit on each 1/0 pin from the flash chip ,
in quad mode its 4 bits on 4 pins , you would need to write your own spi routines for either method ,I think hardware spi is about a good as you gunna get. with a 16f1825 chip I can do 2mbs easy with hardware spi (32mhz clk and for small bursts of course)