The upgraded Mac Pro pushes apps to the limit. In front of me, two 30-in. Apple Cinema Displays glow softly at my desk. Beside me sits the fastest stock-configuration Macintoshthat Apple Inc. has ever shipped: a superfast eight-core Mac Pro. Inside the Mac — and on full display on those screens — is Mac OS X 10.5, better known as Leopard, Apple’s latest operating system. All around me is the work I’ve been putting off that is now getting done.