In the case of blog comments on high PR page, which is the amount of OBL after link is useless or even harmful? For example, OBL 100 good, useless or harmful?
The more links on a page, the less beneficial the link usually is. Some search engines claim they will only index up to 50-100 links on a page. So if there are more links than that, don't expect the link to count for much at all if it does get indexed. This is the reason that high PR blog commenting is a lot less effective these days. Spammers hit up those posts hard and limit the benefits quickly. I'd also take into consideration the nature of those other links on the page. Getting links from the same pages as certain niches can set off red flags.