Consistant steady blogging seems the way to go, where possible adding a quality comment to contribute to the blog.
10 comment per day is enough. But be careful, the Blog should be relevant according to your Website / Blog theme.
I guess the trick is not to look like you are robot doing the submissions - in which case presumably you would struggle to do enough to alarm Google, unless you have the proverbial 1 million monkeys and 1 million typewriters!!
Personally I believe blog commenting is a bad tactic. It got my legitimate site penalised by google within a month of starting the comments. I only did a few aswell, I wouldnt even consider 50 a day.
First thing, which is also forgotten by many, you should comment on blogs that are with quality. If you simply comment on a blog that is not good to the eyes of Google, the result might be bad. Second, you should comment not just for the sake of link building. Your comment must inject some additional points about the topic-- something valuable. Don't just say that's a good article or I agree with you blah blah blah blah. And the third, in the end it's not "how many," it is the "quality" of links you have. Hdwebpros is right, consistency is (the) key!