Which technology should I use to develop a high performance web application
Usually the programming language doesn't really matter. All have their own strengths and weaknesses. All come up with their own best-practices and frameworks.
It's really up to you what's your preference. If you  are coming from Microsoft C/C++ I'd use .NET, if you are from Linux world I'd use Java.
Back in the 90s Java was well known as a slow framework, however there was much of myth and the framework architecture is dramatically changed since that. Today, there is no generally slow or fast framework.
You can find thousands of sites in the web that tell you that the one or the other is faster. However, at the end of the day it depends on how you implemented your solution and how you utilized the best features of the framework.
Greets
Flo
I have couple of ideas in my brain which I would like to bring out before it's too late. Basically I want to develop a web application which I could sell it to clients. So which technology shall I use to accomplish this? I have been a C and C++ software developer but it's been a very long time since I have developed one. So the things I would like to know is:

Scalability and Performance?
Easy way to develop web application in a faster manner?
Any Framework?
Application server?
and which programming language?