Fine on the iPhone 4.
I suspect running the page through a UIWebView as opposed to MobileSafari will introduce the performance issues of application sandboxing.
This was a trap for my iPhone 4 - I couldn't navigate away because it was so graphics intensive. I had to force quit then quickly load another page on startup.
Really? It ran quite smoothly on my iPhone 4S and my parents' ancient Athlon X2 3800+ (running Windows 7). It took 2-3 seconds to get going, but then it was quite smooth.
Totally reminded me of: http://unicodexmas.com/ <- Christmas tree made out of "valid, semantic, and imageless HTML and CSS", ornamented with Unicode characters.