Why would you do that? I agree with others who think AB6 C seats are far behind anything else in Asia, and would not pay for C if flying that aircraft (though service is very good). Instead, in Y I cannot see any big difference to other TG aircraft - generous 34" pitch, no IFE, nice service. So if I'm flying Y I don't see why to avoid AB6 (and I used to be flying a lot with that bird between BKK and DPS).

On OP's question, this might vary between stations, but I noticed that in half-full flights, the A/B and J/K seats are often all filled whereas almost whole middle-sections (DEFG) can be empty. So, especially if you prefer aisle seats, you might have better chance that the next seat is empty if you pick D or G. (Oh, I notice now you are travelling with you wife, so this may not be relevant.)