1)Does L520 / L420 exhibit the same fan pulsing problem as the T520 / T420 (fan goes on and off every 5 seconds or so)?
The L520 has its own fan noise problems so you better watch carefully how Lenovo addresses this issue.
2) How does the 1600x900 for the L520 compare to the same resolution display on the T520 or W520 (as far as brightness, % of the color gamut, contrast ration, etc). From what I read, these displays on T520 and W520 are quite nice.
It is the same display. See FRU no.:http://support.lenovo.com/en_GB/product-and-parts/detail.page?DocID=PD011130#8http://support.lenovo.com/en_GB/product-and-parts/detail.page?DocID=PD008483#HD+