Here is the thing with "optimization", when you look at Mass Effect 3 and say it is optimized, you are full of shit, period. All they did with Mass Effect 3 was take the console settings and transition them to the PC game, tweaked them slightly, and that is it. The game on PC looks almost identical to the game on consoles. If that is what you think makes a game optimized, then I don't think that word means what you think it means.
Now, look at GTA:IV, and what would have happened if they did that. The console settings for GTA:IV were:
Resolution 1280 x 720
Texture Quality Medium
Reflection Resolution Medium
Water Quality Medium
Shadow Quality High
Render Quality Low
View Distance 21
Detail Distance 10
Vehicle Density 33
If they had done what Mass Effect 3 did and used those settings, or maybe slightly higher settings, as the "Max" everyone would have praised the shit out of it for being optimized so well. And remember, the console versions only got 20-30FPS, with those settings my Athlon X2+4GB RAM+HD4670 easily did 50-60FPS. But instead they opened up the flood gates for the engine and let PC uses really max out what it was capable of, and I commend them for that.
So to once an for all answer the OP's question: NO, Mass Effect 3 is not a good example of an optimized PC game. It is a perfect example of a lazy half ass port where they didn't bother to improve the game over the console versions to actually take advantage of PC hardware.
Rig1: System Specs.
Rig2: A8-5600K@4.4GHz / AsRock FM2A75 Pro4 / 8GB Corsair DDR3-1600 9-9-9-24 / HD7560D / Samsung DVD-Burner / 1.5TB WD Green + 3x3TB WD RED in RAID5
Rig3: Athlon X2 4200+ / M4A79 Deluxe / 4GB G.Skill Pi DDR2-800 4-4-4-12 / GT430 / Sony DVD-Burner / 500GB WD
Rig4: Phenom II x6 1605T @ 3.6GHz / Asus M5A99X Evo / 8GB PNY DDR3-1600 9-9-9 / GTX470 & GTX470 / Samsung DVD-Burner / 1.5TB Seagate