You need to say how much memory the card has... post YOUR command line and I'll explain the differences that need to be made.
It's going to be wild speculation - you WILL need to experiment on your own, unless someone wants to loan me one for a week or so, then I'll have the perfect command line
yacminer --scrypt-chacha --worksize 256 -g 1 --lookup-gap 8 -R 5120 --buffer-size 2560 -o stratum+tcp://yac.coinmine.pl:9088 -u username -p password
You've got so many shaders and can't use them all at lower lookup-gap values, so we try here to use them to trade off for the lack of memory by increasing the lookup-gap. 8 is probably a decent place to start (we like 1,2,4 & 8, the others are oddball sizes). I'm assuming you can allocate 2,560 MB in one thread (i.e. you have more than 4 GB system memory - if you don't you are going to have a bad time), and at lookup gap of 8, that amount of memory can only support 5,120 simultaneous threads at N=14, so that's the value for -R.
Another theory would be to try lookup-gap 12 and -R 7168 - I don't think the extra work being don by the extra 2048 shaders will make up for the extra 4 runs through on the lookup gap, but like I said... wild speculation
That's a pretty great rate for a card mining YAC.... compare it to all the cards on the YACoin wiki /index.php/Mining_Hardware_Comparison]http://[Suspicious link removed]/index.php/Mining_Hardware_Comparison and you'll find it compares really really well... Now that you aren't getting HW errors, overclock it until it's unstabe! (and then bring it back down until it is stable...)
enjoy your hash mate - none of my cards get over 3 KH/sec
I will post screenshot after some attempts of tuning