I wouldn't call it "4/3," because AFAIK it's a separate boost. It should give some benefit of its own regardless of whether your Extraction is at 0/3, 1/3, 2/3, or 3/3.
Yes, it provides a small benefit. 12.5% increase drop rate above 3/3 I believe.
Note that this is a pure percentage, not "basis points". So the 5% chance at a gold upgrade temper gives you an extra 12.5% of 5% = 0.625% for 5.625% new chance at a gold upgrade mat. I have talked to multiple people that were furious that they were not getting gold tempers 17.5% of time because they added 12.5 and 5.0 together. Which is somewhat understandable. The game treats percentages as basis points in many situations. The 12% crit chance from Major Prophecy/Savagery adds a flat 12 to your current crit chance. The 10% crit damage from Major Force adds a flat 10 to your current crit damage, and so on. But Meticulous Disassembly multiplies a percent of a percent which is different than many common in-game stats.