Basically ETC rolled back the DAGs so its less than 4GB so you will get the full speed which should be around 28MH/s if you are mining ETC. If you mine ETH right now with that card you will get like 5MHs or slower or won't work at all.

The issue with ETC is that its not very profitable. You get like $6 a day with ETH but with ETC you get less than $2 a day. So its better than nothing but keep in mind that ETC had a huge pump this week. A few weeks bad it was like $0.50 a day or so. So mine while its still profitable.