Damage from Low Oil Pressure

I beleive my 2001 9-3 has just succumed to the dreaded sludge problem. It has 170K on it so I can't complain too much. Had the red oil light come on while driving a couple months ago, with no apparent ill effects(I changed sending unit at that time). Oil Light came on today while driving on the highway, and this time the engine started making noise, so we shut her down and had it towed home. (Oil is full) Now when I start it up, it clatters for a couple seconds til the oil pressure builds up, and then it settles down to a sharp ticking sound, like one lifter is really bad. Its not a clonk, like a rod or main bearing, but rather a loud tick.

The help or advice I need is: where would low pressure first cause problems. Would the valves and cam bearings starve first---and that is the noise I'm hearing. Or would the bottom end be the first to be damaged with lack of oil?

Sorry for the long-winded explanation---any advice would be helpful and appreciated.