But for what you are doing I think you can simply use the same method for the capacitor resistance that you are using for the loop resistance. That will tell you which one dominates, capacitor or loop.
That sounds like a good idea to get ballpark figures.
I recently found this RF sheet resistance spreadsheet which is very
helpful in these kinds of calculations. You can select the material type (copper, aluminum, etc.) and a range of operating frequencies, and it shows you a table and graph of RF sheet resistivity/square for skin depths from 1 to 5. Very informative! http://www.microwaves101.com/encyclopedia/RF_sheet_res_examples.cfm#download
As a quick test I calculated the RF sheet resistance of the surface area of a copper torus using the 5-skin-depth copper resistivity values from the table. This yielded identical RF resistance values with the common small loop efficiency calculators (AA5TB and 66pacific, which I believe both use the ARRL handbook formulas). So the table values seem correct, and allow investigation of various types and thicknesses of metals.
I'm starting to explore electromagnetic field simulation software but it's slow going. For now, the sheet resistance method seems good enough to make sure I'm at least not introducing vast losses with my chosen metal type, geometry, and thickness.