Here's one lesson I learned about parsing on logs. I recently got a 920 ring that wasn't perfectly itemized for me but was still a dps increase. It increased my dps by about 3-4k according to sims. However, it put me into a higher bracket.

As an example, an elemental shaman in 905-907 ilvl bracket can parse 75th percentile on H Krosus with 718k dps (Reference) and a 908-910 ilvl bracket 75th percentile needs 770k dps (Reference).

So, although my ring would increase my overall dps and my parse "for all ilvls" a lot of people are too caught up on the ilvl% so they can say "look how skilled I am compared to other people with my ilvl". So that 3-4k dps increase make me look a lot worse on that scale. I believe ilvl% should just be abolished because the best way to achieve a high ilvl% is to wear stuff that will give you the most throughput while keeping ilvl at the top of a bracket - meaning I look like a better player by using a 900 ring with my best stats (for ele - crit and mastery) than my 920 ring with 2k versatility and 1k mastery.