AVG vs WU

Hello everyone! Im quiet new to cryptos but reading quietely through everything for the past months.

I finished my scrypt mining rig about a week ago.

Im using a sapphire r9 290 on a asrock extreme4 motherboard.
im using a rather old cgminer version : 2.11.4, however i tested 3.7+ and i get a little lower to the same hash.

Latest catalyst drivers and the v 2.7 SDK.

I left the mem clock default at 1250 and increased the engine clock to 947. Intensity set to 20 with thread concurrency 27000.

This way i got pretty satisfieing results with an average of 830 Khs. But now i know that WU is supposed to show you the actual rate that depends on variance and other. So on one side im getting a little confused for whats the real number i should look at. The pool hashrate is not too stable changing from 655 khs to 1200 khs or even 1300 khs, but mostly rangges from 700 khs to 900 khs, AVG shown on cgminer is 830 khs and the WU is 750 avg. When i calculate of what i mined i get to about 800 kh's which is not bad from my sight, could be worse.

However what would i do to get things more stable? Or to improve the WU? It seems like the pools choice is very important.

On some pools i net a WU of 790-800, others below 750 and even 650-690. So i doubt its a problem with the GPU's clockspeed and more a connection problem? But how come im having a very low WU eventhough i dont net any invalids on some pools?

Thanks for your time!