Now remember what pcb just said about Shimano's twist teeth "grabbing" the chain, and imagine how that will work with Accu-7's generous overshift freeplay. Likely there would be some momentary overshifting to the next-larger cog than you are wanting to shift to.

I assume that your GPX gruppo is 7-speed, so if you can get a Hyperglide cassette spaced to Suntour dimensions (I can supply the needed cog spacer dimensions), then a narrower-yet chain (something I wished I could buy back in 1992) will be the ticket to moderate the effects of the generous overshift, the aggressive cogs, and the narrowed spacing between Suntour's larger three 7s cogs.