Severe performance problems

[thedarkmist]

Hello.
I'm going to start a wordpress site, based on the genesis + news child and WPML, which is pretty big:
posts: ~25.000
postmeta: ~180.000
terms: ~2.600
term_relationships: ~34.000
I have performace problems on a VPS Level 4 on Hostgator http://www.hostgator.com/vps-hosting/
Despite I've installed and configuret cache plugins, the site experiments random blocks with CPU going to 100% for a long time, I suppose when accessing a non-cached page. I've accurately debugged all plugins and scripts... all seems fine. Someone can point me in the right direction? Is a site too heavy to manage for WP?
The site is located here: http://www2.parksmania.it/
Thank you in advance...