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It sure would help if you told us which Mac you're using and what year it was made...
 
2010ish iMac 11,1 with Intel core i7, 2.8 ghz, 16 gb memory, ATI Radeon hd 4850...
 
Thanks much - upgrading now to EC and then to HS. What about switching to SSD?

SSD will greatly speed up your Mac and its a good idea.

Given that High Sierra has just been released it might be better idea to wait 2 or 3 updates before installing it. Keep in mind that High Sierra has mandatory new APFS filesystem if you install it on SSD. New filesystem may have issues so waiting may be better choice...
 
10.6.8 --> 10.9.5 --> 10.11.6 --> future stable macOS

My 2010 MBP came with 10.6.3 upgraded to 10.6.8 for stability... 10.11.6 is where I am now.

Waiting for 10.13 to stabilise, else it will remain 10.11.6 forever until I get a new machine...
 
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