Yea.. If u swap them for 2x 980s u'l get a good performance boost...
Titan is arguably better than 780 since it has more raw power packed than 780...
Current top end gpus are ranked as-
980 > 780Ti > 290x > 970 > titan > 780.
Go with dual 980 or wait a couple of months for r9 390x which will easily kick 980's ass according to leaked test benchmarks... And obviously will be cheaper than 980...
Select my answer if it satisfies u...