v=[wf]^(10/3)*c
Meaning the speed of a starship is the cubic root of the warp factor raised to the tenth power multiplied by the speed of light. At Warp 9, this comes out to 729c[cbrt(9)], or about 1,516 times the speed of light.
According to the formula the TOS scriptwriters used:
v=[wf]^3*c
Meaning the speed of a starship is the warp factor cubed and then multiplied by the speed of light. At Warp 9, this comes out to 729 times the speed of light. Either way, that's much faster than your claim.