Hi Tony
It sounds like you were using the standard Windows Multimedia drivers, or a very poor sound card, (Or both) if you have a quality sound card and use ASIO drivers you will find that with the computer you mentioned you will be able to use everything that Hauptwerk has to offer without problems.
Don’t forget all the products you mention can be tested at the Blackpool Keyboard Festival open days, and is a good way to compare before spending your money. (Special deals and pre-owned instruments are also available)
You may also wish to visit the Miditizer website,
http://www.virtualorgan.com (It’s free) its main downside is that it has to run stand alone rather then as a VST.
Enjoy whatever you finally decide on
Bill