How can I fix Kontakt 5 CPU glitches?

Question

So I've been working with Logic Pro 9 (haven't upgraded to X yet) on my iMac for a few years now and in recent months have acquired Kontakt 5 and loaded different sample libraries. And I have now reached a point where I can't deal with the glitches and CPU spikes anymore. Especially when using Cinestrings CORE samples. I can't work well with Logic constantly glitching with playback and Overloading as I try to compose with these libraries. I've looked up countless ways of optimizing Logic's performance and have called Apple Support about the matter and followed their instructions. All my software is up to date, including Kontakt 5. I've tried reloading Logic Pro 9, I've tried freezing tracks, I've tried purging tracks, I quit all other applications when I'm working, I don't run backups when I'm working, and i've followed each of the steps that apple support sent me in the Logic Pro 9 troubleshooting document.
I am wondering if there is a method that could resolve me problems, such as fitting my computer with an SSD to make the application run more smoothly or if it's even worth doing that? Maybe more RAM? And if so how would I go about doing that? I have more than half of my storage space available, but maybe putting some of that elsewhere would be helpful? Or maybe Logic Pro 9 is so outdated already that I need to upgrade to X (but i hear of people having problems with X anyway). Please help.
Here's my computer's tech specs:
iMac
21.5-inch, Late 2013
Processor  2.9 GHz Intel Core i5
Memory  8 GB 1600 MHz DDR3
Software  OS X 10.9.4 (13E28)
(PS. The person I spoke to from Apple support asked for my Logic Pro 9 serial number and my application didn't have it in the place it was supposed to be. The person said this was unusual. Maybe has something to do with my problems. Not sure.)

Answer 1

In addition to Pancenter's comments....
Cinestrings is a heavy CPU usage library for Kontakt.... so the kind of overloads you are seeing based on your system specs.. is to be expected at times..
Even on more powerful Macs than your own, (Like my i7 3.4Ghz Quad Core 32GB 2010 iMac) its quite possible to get overloads in K5 when using it or say some of the Spitfire Libs or LASS for example.. especially when using multiple K5 libraries or other plugins at the same time... unless you manage and setup  things properly.
Its not about LP9 not being good enough........ as performance under LP9 in 64bit mode tends to be much batter than LPX... though under Mavericks you do get a performance hit from OS X itself anyhow... with both LP9 and LPX.  The fastest current combo would still be LP9 and Snow Leopard but your iMac cannot run Snow Leopard as that OS X version doesn't have the drivers for the newer hardware onboard your iMac... and Lion/Mountain LIon had issues with Logic in versious different ways,... so 10.9 is your best bet currently...
Tip: I see you have tried this but... The most practical method to optimize things is often to freeze all K5 or CPU heavy plugins based tracks.... and unfreeze only when you need to edit... Most users of multiple K5 tracks will do this as part of their normal routine with any DAW where freezing tracks is possible.
The fact you are running only 8GB of RAM probably doesn't help.... (I use 32GB when possible and 16GB as a minimum these days on my various Macs)
Also, using the internal HD for everything isn't the best idea either. Get a fast 7200/10,000K/SSD, non Green/non energy saving, TBolt or FW800 (Not USB2/3) connected external HD for your sample libraries for example..and you will find that may help things too...
Example: I picked up a couple of the WD VelociRaptor Twin 10,000 RPM 2TB Raid TBolt drives from Amazon for less than $450 each recently and these things absolutely fly... Faster than most SSDs that I have tested to be honest... and I noticed a good boost in performance and capability when storing my K5 libs on them....compared to my older FW 7200rpm fast Glyphs that I have used for years now...