I too am considering a switch to PS at some future time. My site is also in development.
While someone may have quantified input (perhaps X% reduction in access time), I don't see the decision purely as a numbers evaluation. Shared and PS are different environments. I see three reasons for switching to PS:
1) A site with too big a footprint (CPU, memory usage) will not "play well with others". If performance degrades under load to the point a site impacts the other users on the shared host, DH will likely take action. This may include disabling your site. In this case, PS benefits you by providing a "larger than fair share" of a system compared to the shared environment. If your site grows at some predictable rate, you will be able to choose a time to upgrade to PS, and increase resources as needed. There is an Achilles' heel, though. While the resource allocation is guaranteed, it is also capped. A big spike in visitors will still bring the site to a crawl. At least your former neighbors will not be screaming at support .
2) A site which needs a reasonable level of performance (as defined by the site owner) may be impacted by other sites in a shared hosting environment. Putting your site on a PS insulates your site from the performance hit caused by other sites on a shared system. While there is no SLA at DH, I would expect a PS to provide more stability/predictability when compared to the shared environment.
3) If you want to install/run a service/process not permitted in a shared environment, DH may permit it on a PS.