Very good.
260x(100W TDP and 85W gaming power consumption) is based on a 85W TDP chip(7790, the more power efficient chip of our time with a gaming power consumption of 70W) at its stock clocks(1000Mhz). If Nvidia managed to make a chip with a little power envelope(60W) have the same performance(and more perf/mm²), is their merit. Then the Maxwell card is gonna double the performance/watt of 260x at the same node. This is awesome.
I expect per now power consumption be between GTX 650 and GTX 650Ti levels(closer to GTX 650).
Geforce GTS 450(perf equals 9800GTX+) haves a TDP between 106W and 150W(nvidia not released the data, only states gaming power consumption is 106W). Radeon HD 7750 is 10 percent faster than GTS 450 and is tied with a TDP of 75W(Avg power consumption of 45W) on 28nm.
GTX 750 Non-Ti promises triple the performance of a GTS 450 under sub 75W TDP(and is half of GTS 450 TDP).
GTX 650 gaming power consumption is 50W(half of GTS 450 and with more performance). GTX 650, despise its 6-pin power connector, is a chip with same TDP and power characteristics of HD 7750.
With less or equal GTX 650 power consumption levels, GTX 750 is promising 6x more performance per watt than Fermi, that was maked on the less older node(40nm).