This article is from the Apple II Csa2 FAQ, by Jeff Hurlburt with numerous contributions by others.
Probably not. The new 14MHz 65C816's available from WDC make it generally unnecessary to swap in new GAL chips to go to higher speeds. In fact, one user with the faster GALs already installed reports that his TransWarpGS would not work until GAL 3E was replaced with an older GAL 3A. If you are attempting to use an older 65C816-- e.g. a 10MHz chip released in the early 1990's-- then, it may be necessary to upgrade the GALs (especially GAL 3A) to run reliably above 10MHz. Due to variations in boards and parts, about the only way to find out is to experiment. By: Rubywand