I think that a 2-core processor, 3 GB of RAM, and 100 GB of SSD should be enough to run 5 websites, especially if 2 of them are practically dead and the other 3 have moderate traffic. However, good website performance depends not only on the server and its settings, but also on the optimization of the sites themselves. If you have old and heavy query-heavy websites with heavy image formats (png, jpeg), no super-fast VPS will help you, only a good website developer will. You can check your website on GTmetrix
However, if you don't have any problems with your site and you need the best servers to improve your speed, then you should consider the offers from
hostpro.com. I personally use their hosting and I am impressed with their server stability, loading speeds, and support efficiency. With 5 different websites with different needs, it might be helpful for you to look into their
VPS plans and reach out to their support for advice.
Regarding hostingsource.com, they can be an option too, but I would recommend looking at user reviews and comparing them to hostpro.com before making a decision.