Would students feel uncomfortable if I include in my lecture a quote which is somewhat sexually suggestive?

Avoid, but not for that reason.

Sometimes it is a teacher's duty to do things that may offend members of their class. A biology teacher who avoids the subject of evolution for fear of offending creationists is not doing their job, and there are plenty of other examples. The problem here is not that the joke could offend; it's that it gets in the way of learning.

It treats women as eye candy rather than as thinking beings, implying that a woman's clothing should be chosen for the benefit of male onlookers rather than according to her own priorities.

Whether you actually believe that or not, telling that joke gives students the impression that you do. That perception makes the classroom environment more unpleasant for a female student and less conducive to learning.

Humour has a place in teaching. Used judiciously, it can help hold the audience's interest and keep them engaged. But for your female students, at least, this particular joke is unlikely to serve that purpose. There are plenty of other ways to say it.

I'm familiar with the quote and I understand that it's well-intended. But don't do it. You're asking for trouble. What passed as acceptable 70 years ago does not always fly today.

Honestly, I don't think the woman's skirt part adds anything substantive. You can make your point perfectly well without it. "A good speech should be...long enough..." and so forth. Including the phrase makes you seem as if you do not understand the current bounds on professional discourse.

I don't feel offended, but it makes me question your judgement.