If you're working on a project where I/O blocking is your primary performance issue, Node has a lot to offer in the form of a framework that helps and encourages you to structure your code in a way that works well for such tasks. Javascript's performance and its being single-threaded will have minimal impact, because those concerns are absolutely dwarfed by I/O costs in the situations Node's designed for.
On the other hand, if you're worried about how many threads you can run at once, then you're working on a task where CPU performance matters. That's not what Node is designed for. If you use Node anyway, you've decided to try hammering screws into place - and you should absolutely expect that it won't work out very well for you.
If you're working on a project where I/O blocking is your primary performance issue, Node has a lot to offer in the form of a framework that helps and encourages you to structure your code in a way that works well for such tasks. Javascript's performance and its being single-threaded will have minimal impact, because those concerns are absolutely dwarfed by I/O costs in the situations Node's designed for.
On the other hand, if you're worried about how many threads you can run at once, then you're working on a task where CPU performance matters. That's not what Node is designed for. If you use Node anyway, you've decided to try hammering screws into place - and you should absolutely expect that it won't work out very well for you.