The Pro has 2 of the SATA ports in a position that will make them unusable when a large graphic card is installed, the LE doesn't have that issue. The Pro's 2nd PCIex16 slot is only x1 electrically, so it is useless for a 2nd card.
On the other hand, the Pro has USB 3.0 if that is important to you, plus 3rd party SATA III (Asmedia). The LE does not. Go to the web sites for the 2 boards and compare the specs. Then you can judge for yourself what you feel is a necessity and what isn't.
SATA III (6Mbps) is mainly for Solid Disk Drives (SSD) because they need all the throughput speed they can get. Mechanical HDDs are limited by their RPM and moving parts. 7200 RPM HDDs rated at 6Mbps speeds, can't even saturate the SATA II interface. So there's really no reason to connect a 7200 RPM HDD to a SATAII header... although there's no harm in doing so.
The 'ASUS Fan Expert' feature is usually supported by some other name in all motherboards. It is just an automatic speed controller to lower fan RPMs (and noise) when the fans don't need to run at full speed. But it only works with the fans plugged into the fan headers on the board.
The i3 Sandy Bridge can't be overclocked (easily). Its freq multiplier is locked. And it's memory controller tops out at 1333MHZ. If you buy faster RAM, it wouldn't run any faster than 1333MHZ. You would have to O/C it with setting changes in BIOS. But moving from 1333MHZ to say 1600MHZ RAM provides very little gain in performance, anyway.