A comparison of openSUSE 12.3 against the latest releases of Ubuntu, Fedora, CentOS/RHEL, and other Linux distributions is being worked on at the moment across multiple systems. For those impatient though and wondering how openSUSE 12.3 is performing, benchmarks can be found on OpenBenchmarking.org within 1303139-FO-OPENSUSE183.
Embedded below are just some of the openSUSE performance results from this HP EliteBook Core i5 "Sandy Bridge" reference SDV laptop from Intel. When going from openSUSE 12.2 to 12.3 is an upgrade from the Linux 3.4 to 3.7 kernel, GNOME Shell 3.6.3 over GNOME Shell 3.4.2, X.Org Server 1.13.2 over 1.12.3, Mesa 9.0.2 in place of Mesa 8.0.4, and various other system package updates that have the potential to influence the performance results. Both releases are using GCC 4.7 as the code compiler.
From past testing on other distributions, between Linux 3.4 and 3.7 there are some file-system performance changes for EXT4 and Btrfs depending upon workload and some Intel / Nouveau / Radeon DRM driver improvements. Moving from Mesa 8 to Mesa 9 also yields some open-source driver performance improvements in addition to better OpenGL coverage and other features. Overall, it should be a fairly positive hardware experience in theory moving from openSUSE 12.2 to 12.3. It would have been nice to see Mesa 9.1 in openSUSE 12.3 rather than having to wait another six months, but the 9.1 release was only tagged in late February.
Aside from cases with anti-aliasing and other caveats, yep, Mesa 9 with Intel HD 3000 "Sandy Bridge" graphics show off better on openSUSE 12.3.Computationally-bound workloads generally aren't interesting in this comparison since both openSUSE 12.2 and 12.3 are using GCC 4.7 as the compiler without any major differences.
See the rest of the data in 1303139-FO-OPENSUSE183.