IBM has posted a new article, "IBM PowerPC 970FX power envelope and power management", which details some of the power usage specifications of the G5 970FX.
First, it lists the G5 2.5 GHz 970FX at 100 Watts. This agrees with the maximum power that was predicted in a previous Everything Apple article, and confirms that maximum power value is approximately twice the value of IBM's stated "typical" power value.
Second, it states that there is a limitation in the current G5 design which prevents functionality below 1.0 V. Conversely, it does seem to confirm the chip will function at 1.0 V at reasonable speeds. IBM has previously suggested that a G5 970FX at 30 Watts would make for a reasonable laptop CPU, with speeds up to 1.8-1.9 GHz.