Hi,
the apparent 'additional' resistor/capacitor is not relevant. Two stage means there are two inducive elements and two capacitive elements in the transfer function. In practice the two elements,
both inductors and capacitors, may be realised as more than two each, but the all important transfer function is still two stage, or technically 'four pole Chebyshev' or possibly 'four pole Butterworth', maybe even 'four pole elliptic'
If your line filter has a genuine 'extra capacitor' then it would be 'five pole Chebyshev or 'five pole Butterworth' etc', and therefore better....and you would know by virtue of cost.

Craig

PS: Comes from a lovely piece of theoretical work (Fosters Reactance Theorem) published in 1924 by Ron Foster....I remember it well...it was a Tuesday!!!