The best CPU this series offered: Intel Core i5-680
The CPU in question: Intel Core i7-860S
Take the time to review the differences! The TDP of the i5 is only 73 W unlike the i7 which is 82 W You also will face the limitations of the systems BIOS (EFI) your system uses Clarkdale series chips. Apple wouldn’t have loaded the Lynnfield series information into the EFI so jumping to it will be risky!
As far as RAM 16 GB is the largest tried so again jumping to 32 is risky! Don’t forget if you are jumping to the more power hungry CPU you are likely skating on thin ice as your power supply will be pushed hard with the added load of the RAM. You could lessen the load by removing the HDD and using a SSD instead.
I’m not sure I follow what you mean with 4,1 vs 5,1 are you talking about the EFI firmware updates? Review this listing to find older firmware versions. Apple no longer handles firmware updates this way! It’s all done within the OS installer. So if you are running High Sierra the installer would have updated to a much newer version. Apple does not list the EFI Boot ROM version or SMC version anywhere so you can’t track it (bummer!) So basically forget it! Just make sure you’ve updated the system to the latest MacOS it can support, reference this 21.5” iMac 3.6 GHz Core i5 (Mid-2010)
OK, now the fun part! Your system is only able to support MacOS High Sierra 10.13.x so jumping to Mojave 10.14.x is not possible via Apple. You would need to use DosDude Mojave Patcher
So the last piece is which to do first! I would update the OS to High Sierra and stop there. Next upgrade the RAM to see if you really can get to 32 GB. Do make sure you can return the SODIMM’s if it won’t work to get the others to get to 16 GB. Next I would replace the HDD to a SSD as we need to lower the power draw before you even attempt going to the 860s Lynnfield CPU. Then and only then would I swap out the CPU. If it is working at this point I would then upgrade the MacOS to Mojave. And the very last step would be to replace the GPU.
OK now on to the GPU First you need an Apple board as it has custom firmware. Here’s the part you’ll need AMD Radeon HD 6770M, 512MB - Apple P/N 661-5945. You’ll need to swapper the heatsink from your board as the 6770 board has a larger fin unit. Which gets into the rub here as you’ve boosted this system so far you’ll need to add additional cooling you’ll need to fashion a squirrel cage blower to pull the air out of the top vent externally to help in cooling your overheating system! Frankly I would forgo the GPU update as this will also kill your power budget pushing the power supply to Red!
Understanding your systems power budget
First lets use a more tangible example lets say you have a suitcase and you are going on holiday. Its a smaller suitcase so you are limited on what will all fit in. You put out your cloths for travel and you’ve started to put them in but not everything fits so you need to unpack it and deside what to leave you pull a few things out and pack again. This time you have still have to much so you need to go through the process again this last time everything fits.
Now lets look at your system Apple packet it with just enough power to service the design of the system with a bit of head room. Now as you add things in you are getting close if not over whats the systems power supply is able to serve. So you just can’t throw everything in unless you upgrade the system (suitcase) which is not an option here as Apple never created a more powerful power supply or offered additional cooling for the system.
Thats why your actions are too extreme for this lower end system. Changing out the Hard Drive Disk (HDD) to a Solid State Disk (SSD) uses less power and cooling which is why I have suggested it. Adding swapping out the CPU to a more powerful version and RAM draws more power and creates heat.
So the bottom line here is you overstuffed the suitcase and you need to decide what you need and what you don’t. Thats why I had recommended the order of change. The GPU is the hotter and more power hungry item and I’m suspecting you can live without. If you bought it already then I would recommend you return it.
You added an additional piece of information on what you where thinking. Given what you are planing on doing you only want one drive within it. So forget about the HDD and just put in the SSD.