Seriously? I'd like to see a picture of that page. The compression ratio of the 85-87 Si's was too low to make good use of premium gas... it is a good idea to use it with advanced timing though.

Reconnect the stock vacuum advance and see if it still runs fine. Remember, the stock vacuum advance is there to advance the timing under engine load for more power. It helps more then a simple advance of the static timing (which stays the same regardless of load.)