Therefore, this notion holds, Va would not vary.
From the relevant flight manuals for Va speeds.
Cessna 207 Basic weight in 2200 pounds region.
3800 pounds 130 KIAS
3050 pounds 117 KIAS
2300 pounds 101 KIAS
Cessna 172N Basic weight 1400 pounds region
2300 pounds 97 KIAS
1950 pounds 89 KIAS
1600 pounds 80 KIAS
I would opine that a 17 knot spread represents a substantial proportion of the 172 speed capability, at 75% power, 2000 PA, standard temp, cruise is 116 KTAS. Ignore Va at your peril.