Far more powerful. The only problem is that the 780ti (kepler series) has a far higher TDP and power requirements than the 900 series (maxwell) or 1000 series (pascal). It is a very potent card, but a bit of careful shopping could get you a GTX 970 for around the same price (found one on eBay for $160 - buy it now - free ship).
A GTX 970 would be almost as quick as the 780ti (GTX 970 firestrike - 9200, GTX 780ti firestrike 10400) but at a much lower TDP (150-180w vs 220-250w). So - it's a good card, it's a fast card, and at $150.00 - it's a very good buy (average price is $250ish on eBay). And it's a sure thing. If your PSU is up to it I'd say go for it. You should have a minimum 600w and a GOOD psu.