"What I'm really wondering is if putting the A cam in the '92 will improve the performance..."

Yes it will. The stock M cam is very mild. The A cam will help, as you found out with the 87.
Better yet is to go with a B or VX cam and use an adjustable cam gear to advance the timing. The lumpier cam gives more power in the higher RPM range while losing it in the low end. Rotating the timing brings back some low end. This is all very well documented. The best cam I've used is the Enem V15, but it is pricey and only available from Sweden. Stay away from the RSI cam as it is all top end and has terrible low end performance (too lumpy).
The A cam was never stock in the USA, but was an option in Canada.

Cam info.
http://www.turbobricks.com/resources.php?content=camspec

I cannot stand driving a redblock Volvo with a stock M cam, and have put VX cams (+adj cam gear) in my 245 and 945.

As for the difference in performance between your 87 and 92... Do they have the same ignition system? LH2? Same injectors? 92 will be yellow tops. What are the 87? How dirty are the 87 injectors? That will effect performance a lot.