I think the actual http request to get the information is going to take a lot more than your actual processing. And you don't want to make a lot of requests per second to a website because you could end up doing an unintentional DoS attack (which can be considered trespass to chattels and you'll...
Use Flash when you need the artistic freedom (overall impression,feeling over content) and HTML/CSS when content (the information) is the primary concern.
Search engines don't usually like Flash. Flash also takes time to load.