What are the opimum values of Cl during descent?
I am going to work in SI units for all engineering work, anything else would cause instant insanity on my side. I'll leave the altitude in feet (isn't used) and convert speed from knots to m/s so you can follow the flow easily. Since $C_L$ is unitless it should not matter what units you use in the calculation as long as you are consistent.


Altitude: 34000 [ft] (not used)
$V$ (true air speed): 442 [knots] = 227 [m/s]
S = 112.6 [m2]
$\rho_0$ = 1.225 [kg/m3]
$\frac{\rho}{\rho_0}$=0.322 [-] (from your table)
$\rho$ = $1.225 \cdot 0.322 = 0.394$ [kg/m3]
$\frac{1}{2}\rho V^2 S$ = $\frac{1}{2} 0.394\cdot 227^2 \cdot112.6 = 125\cdot10^4 $[N]
$m$ = MLM = 64500 [kg]
W = $m\cdot g$ = $64500\cdot 9.81$ = $63\cdot10^4$ [N]
$C_L$ = $\frac{W}{\frac{1}{2}\rho V^2 S}$=$\frac{63\cdot 10^4}{125\cdot 10^4}$ = 0.5


I did take full maximum landing mass for this calculation. If you want to apply corrections then note that the $C_L$ value scales linearly with the mass. 

One further note:

I assume your data is derived from ADS-B. ADS-B transmits groundspeed, whilst you should work with true airspeed in these formula's. The difference between them is the tailwind (or headwind) component.