Hi, i must say you got a nice eye to encounter this because most of the bike lovers are just looking it. Answer regarding your query, actually there is a much bigger difference between these two engines, the v-twin has always developed power and torque down low in the rpm range. the parallel develops power with a few more rpms involved, and likes to spin higher. the new bonnies will run to 8,000 rpm if you like.
the v-twin has 1 cylinder behind the other, leading to a temp difference, the back one getting hotter, which has never really been addressed, in the air cooled version.
V-twins are typically, except for buell or ducatic, in a heavy cruiser type bike.
Parallels are in bonnies, thruxs, which handle a bit, and even the triumph cruiser line will out handle a harley, if you like that style.
