A quick google search reveals that 90deg gives a well balanced engine, but a smaller angle is chosen because of limitations in the amount of room you have. The main importance is to have a forcebalance
I've been a mechanic for years and built many different kinds of engines, by far the most common angle for a V-8 is 90 degrees, although there are some that use 60 degrees usually for space savings. Most of the time 90 degree engines produce more power and more torque than their 60 degree counterparts.