Safari 8 has suddenly become painfully slow (Not network related)

Question

Since yesterday, Safari has stopped working properly. Nothing has changed in my computer set up or in the applications that I use. I’m running the latest update (Version 8.0.2 (10600.2.5)) on OS X Yosemite 10.10.1 (14B25). I have a 21" mid-2011 iMac with a 2.5GHz Quad-Core i5 and 16GB of RAM.
Here are the symptoms: Safari lags like a drunk cow. It takes about 9 bounces to open after which it hogs 2 GB of RAM according to Activity Monitor—that’s with two tabs open. Webpages take upwards of 30 seconds to open. Opening a contextual menu can take 10 seconds. Opening a new tab takes 2 seconds. Everything else on the system runs smooth as butter. I’m able to edit video, sling huge files around, edit huge Photoshop documents, run processor-intensive Logic projects and browse the web (in Chrome) at lightning speed. It would therefore stand to reason that this is not a network issue or a hardware issue.
I really want to keep using Safari as it’s been my main browser for years and old habits die hard, but this is just insane. I will leave my rant about the recent nosedive in Apple’s software quality for another post as I really would like to know if there is any hope or if I should sign away my privacy to Google and live in blissful ignorance.
I’ve tried all the tricks I know: emptying the cache, clearing the history, booting in Safe Mode. Nothing helps. This is also different, on the surface at least, from the DNS Cache bug that I dealt with immediately after upgrading to Yosemite. With that bug, the progress bar would stall at 20% for 30 seconds at a time but the rest of the interface remained snappy. This is different. It's like the whole browser got dunked in molasses.

Answer 1

When you have the problem, note the exact time: hour, minute, second.  
These instructions must be carried out as an administrator. If you have only one user account, you are the administrator.
Launch the Console application in any of the following ways:
☞ Enter the first few letters of its name into a Spotlight search. Select it in the results (it should be at the top.)
☞ In the Finder, select Go ▹ Utilities from the menu bar, or press the key combination shift-command-U. The application is in the folder that opens.
☞ Open LaunchPad and start typing the name.
The title of the Console window should be All Messages. If it isn't, select
          SYSTEM LOG QUERIES ▹ All Messages
from the log list on the left. If you don't see that list, select
          View ▹ Show Log List
from the menu bar at the top of the screen.
Each message in the log begins with the date and time when it was entered. Scroll back to the time you noted above.
Select the messages entered from then until the end of the episode, or until they start to repeat, whichever comes first.
Copy the messages to the Clipboard by pressing the key combination command-C. Paste into a reply to this message by pressing command-V.
The log contains a vast amount of information, almost all of it useless for solving any particular problem. When posting a log extract, be selective. A few dozen lines are almost always more than enough.
Please don't indiscriminately dump thousands of lines from the log into this discussion.
Please don't post screenshots of log messages—post the text.
Some private information, such as your name, may appear in the log. Anonymize before posting.