You need to use the software to tweak it further. 900core for a 480 on air is amazing.
You need to stop looking at the MHz and realise different chips and architecure are what counts not just the Mhz.
A 4ghz single core 775 P4 isnt the same as a 4ghz 1366 i7 is it.
If you have a 5870 at 1400core on air please show us a screenshot - with
justforoc3d and your forum user name and the date in a text doc on your screen screen (basically I dont belive you)
reason being the only other clocks much over 1050 core have been subzero