A VPS is often described as being in the middle ground between shared hosting and a dedicated server - more flexibility than shared hosting, but less performance than a dedicated server.
While this is certainly true of high-end dedicated servers - the kind we host customers' VPS on, for example - it is not true that all dedicated servers are faster than all VPS. As a Mammoth VPS customer, you get to use a portion of very high-end hardware: the CPUs your VPS has access to are much faster than the CPUs available in the majority of dedicated servers.
You might also consider the I/O performance. As a VPS customer, you get a small portion of an incredibly fast RAID6 array containing 16 or more hard disk drives. A basic dedicated server will come with 2 drives in RAID1 or even a single drive - this kind of setup is not even remotely close to the read performance of a large RAID6 array.
A second consideration is availability: unless you spend up, a dedicated server will not have any redundant parts. If your dedicated server dies, you will have to wait for someone to physically diagnose the fault and then either replace the part or move you to a new dedicated server.
By comparison, our host hardware has redundant power supplies and a UPS: the chance of our host shutting down is greatly reduced when compared to a regular dedicated server. We also run a number of duplicate hosts, so in the unlikely event that one host does die we can move your VPS onto another host and quickly have your VPS up and running again.
There are also the advantages of a virtual environment to consider. Ever wanted to reinstall the operating system on a dedicated server? Or even just required KVM (keyboard, video, and mouse) access to a dedicated server when it has stopped booting? Depending on your circumstances this can be either expensive or impossible. With Mammoth VPS, either of these options can be undertaken with just a few clicks in mPanel.
A VPS can also have its hardware reconfigured instantly - need an extra GB of RAM? Not a problem with your Mammoth VPS: you can change your resources up and down whenever you like.
Finally, there's service availability to consider - and the best way to increase availability is to run your website on two or more servers. With VPS and our load-balancing feature you can easily increase your uptime at a cost that is still well below a single dedicated server.
The choice is easy: if you absolutely need very high performance, can deal with the inconveniences of dedicated servers, and have the funds available then a high-end dedicated server is what you need.
If not - a VPS is less expensive, more accessible and robust, and more performant than a dedicated server in a similar price range.