Well, first off, it's much harder to make predictions about the quality of one formulation versus another if you don't have access to the formulas. Typically, one can get a few tidbits of information about the composition of the products from either labels or MSDS, but the information is typically very limited. For example, one who is familiar with the various commercially available isocyanates can typically pretty well guess what isocyanate curing agent is being used by looking at the solvent composition, VOC, and wt./gal. on an MSDS or even some labels. Information on the non-hazardous components such as acrylic resin solids is typically much more limited.
For a few broad generalizations, with all other factors being equal, mix ratios that use more isocyanate are typically higher in chemical resistance, and may often have an edge in gloss retention. However, comparison of higher solids (lower VOC) products to a lower solids product may make such predictions less reliable. The main factors that ultimately determine mixing ratios are the hydroxyl equivalent weights of the resins used and the quantity of resin solids present.
With respect to buffing behavior, I would expect that rate of hardness development would be affected by the molecular weight and monomer composition of the acrylic resin used, the solvent blend, and most especially by the accelerator package used in the formulation (eg concentration of certain metal salts). A tradeoff in this case is potlife versus cure rate.
Kenseth's experience using the isocyanate for a primer with a topcoat may work fine in some cases, and not in others depending on the individual formulations. There are some good reasons for a manufacturer to utilize a relatively small number of different isocyantes in a product line, and sometimes two entirely different products may use exactly the same isocyanate curative. Other times, they may be very different. Again, without access to the specific formulations or doing some analytical work, it would boil down to a calculated risk. Availability of good labeling information or MSDS info could definitely tilt the odds in your favor of guessing correctly, however.
With respect to toxicity of isocyanates, the ones used in 2K paints are typically selected to have much, much less toxicity than the monomeric isocyanates they were derived from due to their vastly reduced vapor pressure. Still, they should be handled with respect, particularly owing to the possibility of sensitization if an aerosol containing them is inhaled into the lungs.
I hope these comments are interesting to readers. Let me know if comments on a particular aspect are wanted.