Started my first business in 1974, been going strong since.
My business portfolio is varied. Recent focus has been setting up 10,000+ reqs/sec WordPress sites. Most hosting companies can barely make 10 reqs/sec.
Anyone expert who tells you "WordPress is slow"... Do a 180 + run, as likely their incompetence is pervasive.
For example, SERP Shaker WordPress sites I've been setting up recently clock in at 7,000+ reqs/sec.
In November + December 2014, one of my clients ran sustained traffic, all day, every day of 100,000+ unique visitors/second on a $100/month dedicated server machine at a load of 5%-10% of capacity.
If you site is slow remember, site speed depends primarily on the tuning of the server machine where your site is running.