You may want to check your facts...
970 SLI is superior compared to a single 980, while also costing less. This comes at the cost of power consumption, heat, and scaling.
The former two are not as large an issue with the newer maxwell cards, however not all game support SLI fully, or at all.
No....did you read my post above? A single GTX 980 is about 14% faster than a single GTX 970. Sli lets the cards scale at nearly 100% in some circumstances.
Benchmarks start here and continue for several pages.