VPS server crashes with traffic spikes

Hi everybody,

I’m sorry to take on your time to help out there but I’ve tried many many things to sort my problem out without any success.

I’m running a design inspiration blog called https://www.hautstyle.co.uk

When there is a spike in traffic from stumbleupon the website crashes.
To solver this problem, I’ve purchased a VPS server (a bit better but still crashes), I’ve installed W3TC which again helped but didn’t solve the problem. I now use amazons3 services to for them to handle the images and so on. Again, it improved a bit but still crashes when there is a spike in traffic from Stumbleupon (not massive btw, on average 500 visits)

I’m wondering what can be done now to sort the problem out. Could it be anything to do with plugins I use?
Here is the list of plugins installed:

Akismet
All in one SEO pack
Contact form 7
Extra user details
Facebook Share (new)
Feed statistics
Google xml sitemap
Recent posts
Related post thumbnails
SABRE
Simple image size
Simple local avatars
Text Link Ads
TweetMeme Retweet Button
W3 Total Cache
Wordpress Popular Posts
WP-Optimize
WP-Paginate
WP-PostRatings

If any of you could give any advise that would be greatly appreciated.
Many thanks in advance