an OS #8 has a solid platinum coil hence their cost, the solid coil lasts allot longer then plated coils like the OS A3 (same plug only with a plated coil but often misrepresented as a solid coil plug). in high performance engines more often then not you deform the coil of the plug long before you use it past its useful coil life so a plated coil would be a better choice for value, on your average sport engine the #8 can be a more valuable choice also because of the solid coil they are a better choice for a newbie because they stand up better to abuse at the hands of the inexperienced at engine tuning (both overly rich and lean runs)

the Enya #3s mentioned are extremely good solid coil plugs but are very hot in comparison to the OS #8 and are intended for high temp, and high nitro engines where the higher nitro percentage cools the plug conciderably, they are exceptional plugs in helis. the OS website provides inaccurate information, higher nitro fuel cools the plug and the higher the nitro the hotter the plug needed. but just the opposite for high compression, the higher the compression the hotter the plug, so a high compression engine running on FAI fuel needs a hot plug as well.

as the others said the washer is necessary, it prevents the plug from loosening, the only time you don't use them are in turbine engines.

kc

EDIT: just an FYI, glow plug heat range changes the timing of the engine, a hotter plug causes combustion to retard (combustion is further before TDC) and a colder heat range advances it (closer to TDC), can make allot of differences in conjunction with engine compression and fuel nitro percentage.