In this question (link) @PeterKämpf asked me to give a basis for my results. I will share my method for estimation here to see if you guys agree it is correct and how I can improve on it. Note that I use ISA equations where relevant.
Firstly, I estimate the Breguet constant from the PL-R diagrams of the A319-100 and B737-700 (found in the airport planning manuals). For that I use this equation, which is essentially the Breguet equation applied between points A and B (A being MPL+MTOW, B is MTOW+MFW):
$$ K_{sem,i} = \left( \frac{R_B - R_A}{\ln \left( \frac{OEW + PL_A}{OWE + PL_B} \right)} \right)_{sem,i} $$
From the PL-R diagrams: A319-100: R_A = 1463 km, PL_A = 15825 kg, R_B = 5800 km, PL_B = 3800 kg, OEW = 41100 kg (weight variant 00). B737-700: R_A = 3956 km, PL_A = 16860kg, R_B = 6236 km, PL_B = 10800 km, OEW = 38342 kg. — Results: K_A319 = 18277 km, K_B737 = 19607 km.
Using the definition of the Breguet constant, I can estimate their average aerodynamic efficiency, with the following equation:
$$ \left( \frac{L}{D} \right)_{sem,i} = K_{sem,i} \left( \frac{gc_{j,cr}}{V} \right) $$
For that I need cruising speed (A319: M0.78 at 11900m ISA = 230.15 m/s, B737: M0.785 at 11705m ISA+10ºC = 236.91 m/s) and sfc in cruising conditions. I have sfc at 35000 ft and M0.8 16.98 mg/Ns for the A319 and 17.02 mg/Ns in the same conditions for the B737). I adjust the sfc to cruising conditions using the following proportionality (note that beta = 0.5 for turbofan engines):
$$ c_j = \text{cte}(M)^\beta \sqrt{T} $$
I get adjusted values of 16.68 mg/Ns for the A319, 17.2 mg/Ns for the B737. Average aerodynamic efficiencies come out at 13 and 13.96, respectively. I can calculate the average lift coefficient using L=W:
$$ C_{L_{sem,i}} = \left( \frac{2 \frac{W_{cr}}{S_W}}{\rho V^2} \right)_{sem,i} = \left( \frac{2 \cdot 0.8 \frac{W_{TO}}{S_W}}{\rho V^2} \right)_{sem,i} $$
where I've estimated average cruising wing loading as 80% of take-off wing loading. The take-off wing loading of the A319 is 5129 Pa and for the B77 it's 5485 Pa. Density is in cruising conditions. Average lift coefficients come out as 0.4906 and 0.5023, respectively. Using the definition of the polar curve, I calculate CD0 using the following expression:
$$ C_{D0_{sem,i}} = C_{L_{sem,i}} \left( \frac{L}{D} \right)^{-1}_{sem,i} - \frac{C^2_{L_{sem,i}}}{\pi A_{sem,i} \varphi_{sem,i}} $$
where I've taken $\varphi = 0.9$ for both planes (since they have winglets). The aspect ratio of the A319 is 9.5, 9.4 for the B737. CD0 comes out as 0.0274 for the A319 and 0.0265 for the B737. This is off somewhat from the 0.014-0.02 range given by Torenbeek for high-subsonic jets.
Excuse the length, but hopefully you guys can help me improve this estimation or detect errors.