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It sounds like you have a good understanding of how they can be modified. It never felt like an especially fast machine when new, but with an SSD I imagine it would be quite usable for most tasks. The display on mine is a disaster, but for non graphic related work that wouldn't be an issue. It's a pity they can't run anything newer than El Capitan, but not the end of the world right now.
 
mine will be running high Sierra when I'm done.

they CAN run Sierra and high Sierra.

there is a patcher tool to get it running.

Hope to do mine soon when bits arrive (the wifi cards needs changing as not Sierra supported).
Will be posting up here what/how I did it (although already posts here) to help anyone else.

I work for a computer repair shop, but I'm NOT one the engineers I do mainly retail sales but I learn alot from the engineer.
 
I'll be curious to read that. I knew about the patch but didn't think it worked on the 2007 iMac. I actually have a plugin wifi adaptor but it may be too old for High Sierra. I had a 2009 Mac Pro at one stage and unbelievably it didn't come with built in wifi.
 
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