best cutting fluid/oil/paste 2004..... theory and practice?

Hmmm...you specified in some detail, how you want the answer, but you didn't tie-down the question well. And you posted to a variety of hobby groups and a few pro groups.

Oh well.... Water works for some material, kerosine for others, oil for this and emulsifying oil for that.

If you haven't seen it then you might try:

Here are some factors I identify as possibly being important depending on circumstances.

Machining functions Speed, feed and depth of the cutting operation Type, hardness and microstructure of the metal being machined Lubricity Cooling Coolant's applicable temperature operating range Optimal concentration and pH ranges Dimensional control of parts Surface finishes Machine tool maintenance costs Tool wear Downtime for tool and wheel changes Power draw Noise Range of compatible materials Tramp oil rejection Ability to settle out solids Emulsification capability Noncutting functions Corrosion inhibition Fluid residues Flammability Filtration Toxicity Recycling Resistance to bacterial growth Operator Acceptance Operator safety Dermatitis Odor Feel Appearance Financial return Effect on production costs Purchase price Effective life Usage over time Disposal &/or recycling Tool and wheel life Coolant properties Ease of fluid maintenance and quality control Ability to separate fluid from the work and cuttings Storage practices Surface tension Hard water resistance Densities Biodegradability Capacity of recycled coolant to prevent galvanic attack Stability Foaming nature and resistance Precipitation properties Ease of disposal