Going straight ahead, the power steering pump absorbs about 1/4 horsepower. I know that "every little bit helps" but if you are serious about eliminating the parasitic loses from you power steering pump, you should probably install a manual gear. Otherwise, I doubt that your ET slips will ever show the difference.
The above having been said; with an additional 40+ years of experience, when I raced my new 396 1965 Impala I used to crawl under the front and remove the power steering pump belt.
JIML82