A video and blog post at AppleiPhoneInfo.de (German) pits the Apple iPhone against a Nokia E61i in web page load speeds. The iPhone, of course, uses the EDGE (2.5g) network while the Nokia uses a faster UMTS (3g) network.
Despite the network differences, the website load times compared between the two were not that different, demonstrating that the iPhone's rendering capabilities far exceeded the Nokias.
Indeed, in my own experience, in moving from the Treo 700p (EVDO) to iPhone (EDGE), I found general web browsing on the iPhone to be a subjectively faster and more pleasant experience. That being said, the iPhone coupled with a 3G network would likely be far better.