a man having 4.5" penis he can enjoy the sex

The quick answer: yes, absolutely.

Here is a more detailed answer from the Kinsey Confidential (from the Kinsey Institute):

"In a recent study conducted by researchers at IU, men reported length sizes between approximately 3 and 12 inches in length, though other research studies have included men of smaller and larger lengths as well. Circumference varies greatly too. Further, men of all penis sizes can have satisfying, pleasurable and exciting sex lives. The size of a man's penis is not necessarily related to his ability to please his partner nor is it related to his masculinity."

"In fact, though many men often wish for a longer or thicker penis, it is not always easy for a man to have a larger than average penis. Such men may find it challenging to find a partner who can comfortably have intercourse or perform oral sex on them, although variations in positioning and technique, as well as the use of personal lubricants, may be helpful."

"Fortunately, many men — like many women — tend to develop increasing comfort with their bodies over time in terms of the way that they look and function."

You may also find this information helpful, regarding what men and women have to say about being sexually intimate with a man who has a smaller penis (the summary: they all say "it's really not the size, but how it's used"):
http://www.goaskalice.columbia.edu/1360.html