Shane is giving excellent advice to the casual mechanic. The great advantage of always using OEM parts is that you don't have to think. For some people this is a potentially life-saving benefit. Once you throw away what the OEM engineer did and go your own way, then
YOU are the engineer. That is not necessarily a bad thing but there is the possibility that you may suck at it. The fact that an improperly selected tapered roller bearing used with the OEM seal doesn't work does not imply a general problem with the use of a tapered roller bearing in a steering head. I rebuilt a 1971 Honda SL350 for my brother and it had those dag-diggity-danged loose balls in it. There was NO WAY I was putting them back in. Just wasn't going to happen.
Old OEM loose ball bearings...
Since my new bearings were shorter than the OEM, I had to measure the reduction and raise the inner race the equivalent amount with a spacer to recreate the original stack height and prevent any binding, seal fit, or thread take-up issues.
The proper thickness spacer is located between the OEM lower seal and the bearing inner race. The new OEM spec seal is completely happy with all this...
As far as resisting a pressure washer, not even OEM wheel bearings can stand that abuse. The correct approach there is to banish pressure washers from the vicinity of any motorcycle. Pack the steering head with marine grade grease and maintain it occasionally. It will outlast you and the motorcycle with a bit of maintenance.