Clusters have always been 95%, though I'll admit that everything else at 50 was at 90%, at least the one-star materials. Can confirm I had 95% base chance with 347 gathering on Spruce Logs, Grade 4 Carbonized Matter and Prickly Pineapples at least.

This does mean that you can get away with 550 GP, using Field Mastery/Sharp Vision I in tandem with Blessed Harvest/King's Yield II for 100% success rate. Hail stuff!