Metrics similar to Gross Profit Margin in the efficiency category include:
Debt / Equity - A ratio that measures the level of the debt relative to the book value of common equity.
Debt / Total Equity - A ratio that measures the level of the debt relative to the book value of total equity.
Degree of Financial Leverage (DFL) - The degree of financial leverage measures the sensitivity of a company's earnings per share to fluctuations in operating income, as a result of changes in its capital structure.
Interest Coverage Ratio - A ratio used to assess a firm's ability to pay interest expenses based on operating profits (EBIT).