Rich GUI dilemma - web or desktop application?

I'm planning additional visualization tools for diagnostic system. The have "additional" role - because will be scarcely used only by expert users. It's a kind of fancy interactive scatter plot with plenty of displaying options including simple data transformations.

Primarily I thought about it as a desktop application. But I when I get initial requirements it seemed that there is no much functionalities and it could be written as module of already existing web application for data gathering.
I have to gather more details , because now I have to guess future boundaries of that part of the system.

The basic pros and cons array:

	Pros	Cons
Web application	- its web application so you need only web browser (maybe Java or Flash runtime automatically downloaded by browser)- easy deploying - better (seamless) integration with the rest of the (web) system	- possibly low client performance depending on used technology
Desktop application	- established for rich GUI - more computational power to use on client side (really?) - targeted for more functionality "richness"	- target client system dependence (but I know that 99% of users uses Windows platform) - loose integration with the rest of web based system (deployment architecture allows it)

Reviewed technologies and solutions:

• Java desktop app
• Java applet
• GWT application
• YUI components
• flash components

Final choice depends on the range of features, and final users preferences. Web version seems more performance constrained - but there are many technological solutions that make that choice as good as its desktop counterpart. At that point there are very little differences between web or desktop deployment outcomes. Nowadays buzz is "web is the future". I have to make my choice based on economic assumptions.