Small update, as I received an order of 8x16x5mm bearings from Avid RC. Here is a quick look at what they look like installed. I went with rubber on both sides and feel they are a solid product:
Emaxx 3908L, Gorillamaxx G4 with UE VBS & Widetrac, Gorillamaxx G1 with RC Monster Slipperential, Centralemaxx Ph@ntom, FLM Savage, TTR Centurion LTD, TTR Tremor, TTR Ripper Pro, GMADE Stealth