The President shall develop guidelines for preparing nonbinding preliminary allocations of responsibility. In developing these guidelines the President may include such factors as the President considers relevant, such as: volume, toxicity, mobility, strength of evidence, ability to pay, litigative risks, public interest considerations, precedential value, and inequities and aggravating factors. When it would expedite settlements under this section and remedial action, the President may, after completion of the remedial investigation and feasibility study, provide a nonbinding preliminary allocation of responsibility which allocates percentages of the total cost of response among potentially responsible parties at the facility.