Help!! Maximum buffer memory device

hello, i have the following problem:

I have low hash rate (520-580) depending on the configurations, but the only one which reports HW=0 gives me a hash rate of 520.

My bat file is this:

setx GPU_MAX_ALLOC_PERCENT 100
setx GPU_USE_SYNC_OBJECTS 1
-w 256 --thread concurrency 17920 -g 1 -I 20 --look-gap 2 -v 1 -d 0 --shaders 1792

I have a shapphire hd 7950 vapor-x 3 gb

I've overclocked my 7950 with shapphire trix:

GPU Clock 1100
Memory Clock 1500
VDDC 1131

My cgminer said me this:

supports says 803209216
Your script settings come to 1178599424

This has a relationship with my RAM ? I have 4 Gb

Another problem is that I could'nt increase Thread Concurrency more than 17920 because appears me a kernel error.

Anybody could help me ?

Thaaaaaaanks a lot