I performed some tests to compare eMMC with NAND. With the new RK3288 it makes a big difference depending on what chip is used for storage.
The RK3288 box I tested uses Sandisk's SDIN7DP4-16G which is slated to perform at sequential read of 90 MB/s and write of 45 MB/s (see http://download.siliconexpert.com/pdfs/2013/3/3/7/13/47/322/sndk_/manual/sdin7dp4-16g.pdf) except it doesn't!
Other RK3288 devices are using Samsung eMMC and depending on the storage capacity, big differences will be encountered:
8 GB KLM8G1WEMB-B031 read of 100 MB/s and write of 6 MB/s vs
16 GB KLMAG2WEMB-B031 read of 170 MB/s and write of 11 MB/s vs
32 GB KLMBG4WEMC-B031 read of 200 MB/s and write of 50 MB/s
For a table that illustrates the point, please see https://plus.google.com/109451178006683865932/posts/MicuuyJdbak.