Going from PR0 to PR4 is no big deal. I've had sites go from PR0 to PR5 in a single update
I think it's good to remember though, that other people also have sites showing PR0 that will soon be at least PR3 or PR4
I have quite a few of those. I don't exchange links by PR though, I am looking for on-topic pages to exchange with. If you have niche specific pages, please let me know and maybe we can work something out.