generally indica's produce more.
Like you said, there is no way you will know from the beginning... TRY NOT TO THINK ABOUT IT! often growers over estimate the final dry weight and are dissapointed.
If you're new to growing, dont EXPECT anything. Well i mean, dont expect that your going to recieve 700-800 g/sqm. It can be tough getting the conditions just right, and sometimes very expensive.
Now im not saying you WONT get that, but IMO its better to not predict, just to take it as it comes.
one of my first grows, i expected a pound. I ended up with 6 oz. almost a third of what i was expecting. And it can be dissapointing.
On the other hand, it was enough to last me until my next grow was complete.