Hey there, I just recently setup my R9 270 - Gigabyte.

I'm using CGMiner 3.7.2
With a .bat file containing,
 
setx GPU_MAX_ALLOC_PERCENT 100
cgminer.exe --scrypt -u workername -p password -o pool address -w 256 -I 17 -g 1 --thread-concurrency 15508 --temp-target 75 --temp-cutoff 82 --auto-fan --no-submit-stale

Also, have latest Catalyst driver and SDK v2.9.

Good luck, hope this helps you.

Zeak

I get 420 kH/s without overclocking.