I think the flat bar versions are slightly cheaper in general, but the 540 has slightly better spec elsewhere on the bike compared to the 520, specifically having tiagra components. The frame is the same though so I thought you might like to compare riding position. I know quite a few people with Btwin road bikes the old triban 500 (which this is an updated version of) and 300 will last for ever and are really exceptional value.
Im not the best person to ask about the 32 vs 36 spoke wheels, I assume the 36 will take more of a battering though 32 is also very solid.
I think the flat bar versions are slightly cheaper in general, but the 540 has slightly better spec elsewhere on the bike compared to the 520, specifically having tiagra components. The frame is the same though so I thought you might like to compare riding position. I know quite a few people with Btwin road bikes the old triban 500 (which this is an updated version of) and 300 will last for ever and are really exceptional value.
Im not the best person to ask about the 32 vs 36 spoke wheels, I assume the 36 will take more of a battering though 32 is also very solid.