I happened to be perusing the OldVersions SIGHT and came across this article on Opera. As Opera is my preferred browser i was pleased to be forewarned about doing the upgrade that is mentioned.Perhaps it will be helpful to other members.
http://www.oldversion.com/blog/oh-my-what-have-opera-done/
truenorthHi truenorth. I experienced the problem of HIGH CPU RESOURCE usage when I upgraded to Opera 12. So, I switched Firefox for awhile. Now that I have Opera 12.02, the latest version, Opera seems to be performing like the last 11.xx version I had before upgrading to 12.0. In other words, Opera seems to have got the message from user complaints and resolved the problem.

Actually, I've encountered the same phenomena with Firefox; in other words, a new release being PLAGUED by high CPU and/or RAM usage and Firefox resolving the problem with a later release.

Edit:
The comments in your link included comments about problems playing streaming media on websites such as youtube. I've experienced spells of sluggish/choppy video but it has usually seemed to affect any browser I use on my Windows 7 system which is just a Pentium 4. I've found that running CCleaner not infrequently to clean browser history really helps prevent the problem; since CCleaner will clean all browsers during its scan, it's a convenient tool to use for this. The key to both browsers is to turn off auto updates and wait a week or so and check the Forums for issues...
I'm kinda against any updates being shoved on my system with any product...
But that's just me...Quote from: patio on October 09, 2012, 09:30:51 AM

The key to both browsers is to turn off auto updates and wait a week or so and check the Forums for issues...
I'm kinda against any updates being shoved on my system with any product...
But that's just me...

I agree. I find Firefox especially aggravating with regard to updates. They make controlling the updates by the user way too difficult.