I'm not sure I understand the question but I'll take a stab at it.
(Ignoring inefficiencies) 50W is 50W, no matter if it is 12 or 24V DC or 120 or 240V AC. So, with (2)x50W panels, you are getting 100W into 24V or 100W into 12V, and taking 100W out at 240V AC would be 100% of power used in either case.
The advantage to a 24V system is that the inefficiencies are less. While the power is the same, since power is volts times amps (put another way, amps is power / volts), you will have 1/2 the amps in a 24V system than in a 12V system with the same power transfer. Since the power lost in the wire is proportional to the square of the current (loss = amps^2 * resistance), you either have less loss with the same wire or you can use smaller wire.
For example, with a 96W (easier math ;-) panel array, this will be 8A into 12V or 4A into 24V. If you have a wire that has 0.2 ohms of resistance (10 AWG for 30m both ways), the loss of the 12V will be (^2*0.2=13W, where the 24V will be (4)^2*0.2=3W. This is a big difference !
The advantage to 12V is that you can upgrade in smaller chunks (1 solar panel or 2 batteries vs. 2 solar panels or 4 batteries for 24V) and there are more appliances available for 12V.
Stay with 24V (or consider 48V); you won't be sorry.
Dave