On standard figures, a stock 350Z weighing in at 3400 pounds carries 12.3 pounds per 1 bhp (excluding additional equipment and weight of driver). A stock 260Z 2 seater (2425 pounds) carries 14.97 pounds per 1 bhp, even assuming that the quoted stock SAE figure of 162 bhp is true (which most 260 owners would have to admit is slightly inflated). BHP quoted as flywheel figures based on manufacturers claims...
Stock 260Z would need an extra 34 bhp to match the 350Z. For comparison, a stock 2300 pound 240Z with 151 bhp equates to 15.23 pounds per 1 bhp, needing another 36 bhp to match the 350Z figure.
Thus you might reach the conclusion that looking at manufacturer's claimed horsepower is not a very reliable way of assessing the situation. In 240Z days the quoted 151 bhp is reasonable; the later 161 bhp for the 260Z is not!
Autocar quoted 350Z 0-60 mph at 5.8 seconds for the 350, 8.0 for the 240Z and 9.9 for the 260Z 2+2. Motor quoted 8.8 seconds for the 260Z 2 seater.
Not considered in this argument much, but the European 300ZX Z32 2+2 with manual box weighs in at 3495 pounds (Hutton - Enthusiast's Companion) which equates to dragging pretty much the same 12.48 pounds per 1 bhp as the 350Z in 280 bhp Euro spec. 0-60 is quoted at just 1/10 second quicker than a 350Z.
Arguments must come down, therefore, to handling ability and driver ability when making track comparisons. In a straight line race, the results are cut and dried - Z32 fractionally ahead of 350Z at 0-60, with 240Z 3 seconds behind, 260Z another second back and the 2+2 a second behind again!
0-100, the 350Z will ease ahead of the Z32, 240Z will be more than 10 seconds behind, 260Z 12 seconds and the 260Z 2+2 wheezing at more than 16 seconds adrift. On top speed, the 260Z 2+2 gives up first at 120 mph, then 240Z at 125 and 260Z 2 seater just ahead at 127. Both the 350Z and the 300ZX go on to top 150 mph with the 350's limit being a fraction higher than the Z32....
Note again, all comparisons stock vs stock from available sources. Real world variables may apply. Not all cars match manufacturer's specifications. Autocar and Motor are well respected journals and their figures are generally quoted as accurate. Ray Hutton is a well respected author and authority on the Z Fairlady models. Lardy drivers will affect real world figures...