Since there are a lot of very good arboretums in that area, I'd ask them. I'd start with the elephant in the room - Longwood. I'd also not take the supposed rezoning too seriously. Extreme SE Pennsylvania has been considered zone 7 ever since they first invented USDA zones. Valley Forge may have been zone 6 for some of that time, but Longwood definitely wasn't. Any place that considers a temperature of -3F front page news, in about the largest type I've ever seen in a current newspaper, is not zone 6.

A great many plants native to the Pacific coastal area of the US simply do not fair well elsewhere in this country. The climate differences - not just hardiness issues - are substantial. Very generally, if it is not a plant available for sale in your better, larger retail garden centers or in public gardens, then chances are very good it will not thrive in your environment.

Pacific wax myrtle is very much a maritime plant - the further inland one travels even here in western WA, the more difficulty one has in growing PWM and the more likely it is to be damaged by winter cold. While it is usually listed as a zone 7 plant, a severe zone 8 winter can cause problems or at least significant dieback.

Have you considered Myrica pensylvanica or northern bayberry? I realize it is decidious to the PWM's evergreen foliage but it does make a decent hedge. I think mad's suggestion to visit some arboreta or public gardens in your area is very well advised - that would be the ideal place to see what is used in your area, what will be sufficiently hardy and what you like.

Hey thanks for the responses. I was out of town and couldn't respond. I will take the advice. Makes a lot of sense. Many thanks!