We had not looked closely at running the Jaunty Jackalope with older hardware. In this article though we have done just that and carried out a number of Ubuntu 9.04 tests using an older VIA-based PC. More here
Ubuntu 9.04 had booted significantly faster than Ubuntu 8.10, but when it came to the desktop performance with this VIA Nehemiah system with 512MB of system memory, the performance was close between the two most recent Ubuntu releases. In several tests Ubuntu 8.10 was faster than Ubuntu 9.04, but the leads were very small and would likely go unnoticed by the desktop user.