Seeing both types have been mentioned I want to clarify that there is no distinct advantage/disadvantage between a 600 and 750 Shadow beyond fit(how well it fits you) & finish. Neither has a performance advantage over the other, at least not when comparing same generations...the Gen-1 600 & 750 offer identical performance as does the Gen-2 600 & 750. Gen-1 of either will outperform Gen-2 of either.
The differences? Gen-1 models have dual carbs, Gen-2 models have single carbs (and in the case of 750, later models switched to FI). Regardless of intake, the Gen-2 750 also has a shaft drive that hampers performance next to the Gen-1 chain drive.
In other words, the four speed on the 600 is a negligent issue against the 750 five speed, the performance differences don't come into play until you compare generations.