No-one here will be able to give you a definitive answer as Google don't release that kind of info. Obviously, the higher the PR of your incoming links, and the lower the number of links on the pages pointing to your site, the better.
It is also believed that an exponential amount of links (or the PR value of those links) is required to go from PR0 to PR1 to PR2, etc. Therefore, several PR0 links to your site may get you off the mark but you are going to need thousands of them to get a much higher PR, whereas a large handful of PR7-9 links may be enough achieve the same thing for you.
Dont forget, if its true that Google holds back your links due to the sandbox it may take a while for the true value of those links to pass over to improve your site PR.
I must admit that i do think that if your site is of quality it can still rank well with or without high PR anyway.
In the meantime, one way to secure new links is to register with DMOZ.org, it may take a while but once in you will gain good links from all the directory sites that the DMOZ site feeds.
