To improve browsing performance, is it worth upgrading to iOS 5, on the original iPad 16GB Wifi?
The version of Safari that ships with IOS 5 has much better performance than the versions that ship with iOS 4, as reported in this blog post and this article. This increased performance may address the checkerboard rendering issue that you've mentioned. HTML pipelining was introduced in iOS5, and may help with the latency that results in slow rendering. Anecdotally, viewing web pages in Safari does seem a lot faster after I upgraded to iOS 5.

Regarding a rollback to iOS 4 if you don't like iOS 5 - cksum's provides some detailed info in this Apple.SE answer.