I performed this replacement on my iMac11,3 2010 27" A1312, and "upgraded" to a X3470.
The results were unexpectedly POOR. In fact, the machine operated SLOWER than with the i3-550. After experiencing this, it seemed that the appropriate upgrade path was the recommended one. I bought the i7-870 chip and immediately saw the performance gain I had hoped for.
Here are my Geekbench 4 metrics for an iMac11,3 Mid-2010 27", running macOS 10.13.6, with 16Gb RAM on a 1Tb Samsung 850 EVO SSD.
i3-550: Single-core: 2419, Multi-core 5016
x3470: Single-core: 1238, Multi-core 4180
i7-870: Single-core: 2893, Multi-core 9324
While the specs suggest the x3470 to be superior silicon, my experience with a simple 1 for 1 for 1 swap demonstrated a significant reduction in performance. The Single-core index helps explain why my iMac became sluggish, but doesn't explain why things slowed. I bought the i7-870 on eBay for ~ $25... and fully appreciate the maximum performance this older machine can still deliver.
Leo - Are you looking for the information on how to upgrade your CPU?
I don't believe any iMacs have removable CPUs. Am I mistaken?
It's not a matter of faith.
based on the facts.
question to people who have made such exchanges, as I
Alex - For future reference you posted a Question in the place where only Answers belong. Please use the add comment link to the appropriate Answer, Question or create your original Question.
You are mistaken some iMac's have CPU's that are not soldered to the logic board... but it is a PITA to get to them and change them for a few GHz speed benefit (not noticeable for most users of iMac's)
All of the older desktops do. The latest iMacs Thin Series have some that don't. And, all of the laptops don't have removable CPU's or GPU's