Only High PR, is it ok?

Is it ok if all my backlinks are from sites that are PR4 or more or do I also
need lower PR sites linking to me?

I personally think it is good to have a wide variation of links. When building links it is always a good idea to make it look as natural as possible.
Just my opinion.

Agreed, mix a few PR0 PRN/A in there as well, and also make sure to include nofollows too. The point is to make the linking look natural.

Well there are two logics:

1. Mix backlinks with many PR0, nofollow , etc... and increase
the likelihood of being banned (if you landed on a blacklisted blog or a blog that has a very high spam rate)

2. Use only high PR and risk being seen as unnatural or not mixed enough by google bots.

As far as I can see, there are risks in both cases. but 2 is less effort.

Lol 2 is not less effort.. 1 is easy with scrapebox

I mean 2 is less effort if you do it manually, which is what I do. SB has a low penetration rate and your comments are more likely to be deleted or mixed up with the wrong content. That's just my opinion. I don't consider what I do to be spamming and I don't like it to look as such. I actually add to the blog. I read the blog entry and post a reasonable comment, I also add a link to my site, but that's what the url input box is for isn't it.