I have shot with the Ai f/3.5 and the Ai-S f/2.8 version.
Believe me, the f/3.5 version is as sharp as it gets and only a tad slower then the f/2.8.
Also, given the "un-sexyness" of an f/3.5 lens, you'll catch them on ebay for $75 or so. Best darn $75 you'll ever spend.
(here is an old post of mine of over a year ago: https://www.nikoncafe.com/vforums/showthread.php?t=63744 ).