Thanks Claymore!
It seems 3GB cards won't be able to mine ETH/ETC in Windows10 soon because this OS reserves about 20% of GPU memory size and there is no way to fix it (at least easily).
In next update I will set zero devfee for these cards (same as I did for 2GB) so you can mine ETH forks.
If you still want to mine ETH/ETC on 3GB cards you should use Windows7 or Linux.
Amen. My 3gb card is running fine on win10 as long as I have 2x or more 4GB amd cards before it with no extra command line options (on 371 or 369 or whatever was posted) Maybe that wont last either. Luckilly im building a win7 rig just to be more stable for mining.