Will a hysterectomy have a significant impact on a woman's ability to achieve an orgasm or is that a myth?

Myth. This is a myth. Several studies have debunked this. Having the uterus removed during hysterectomy has no long term effect on sexual function.
Sex after Hyst. No. In fact, most women who have the surgery to deal with chronic pain or bleeding or pelvic pressure (such as from fibroids or an enlarged uterus) find sex easier, once the pain and bleeding are not an issue. Talk to your doctor if you have specific concerns or if you are having your ovaries removed at the time of hysterectomy.