Titans do around 200k-220k PPD depending on the OC. 780s do around 160-190k PPD depending on the OC. I'm not sure the extra 10-30k PPD is worth an extra $350 initial cost to me, but in theory it does offer more points over an extended period of time.
One thing to think about is the R9-290X that is supposedly dropping Oct 15th, or near there according the to rumors I have read. That should have ~2800 SP vs the ~2000 of the 7970, on the current WUs 7970s do around 115-130k PPD, so with the extra SPs that number could be closer to the 200k+ range. According to the rumors I have read the price point will probably be pretty close to the GTX 780.