Hash difference between cards

Hi,

I am running 2 x XFX R9 290X and currently get 850Kh/s on one card and only about 700Kh/s on the second with this CGMiner command line (both about 92 degrees) :-

C:\Users\Mining\Downloads\Mining\cgminer-3.7.2-windows\cgminer.exe --scrypt -o stratum+tcp://eu.wemineltc.com:3333 -u username.1 -p x -I 20 -g 1 -w 256 --thread-concurrency 32765 --gpu-powertune 10

I, therefore, have 4 dvi ports (2 in each card) with a single monitor plugged into one of those ports and have read a million things about performance (and differences between cards) such as having a monitor plugged into one port and requiring dummy plugs in the spare ports but does anyone know if these still apply to the latest cards?

Should I be happy with those numbers?

I have tried adding these params but CGMiner refuses to start properly :-

"gpu-engine" : "1025",
"gpu-fan" : "40-100",
"gpu-memclock" : "1350",

Any thoughts or advice gratefully received.

James.