Unvanquished Alpha 49 is also special in that it brings a new, tile-based forward+ renderer, which should help significantly with lighting performance. There are also patches to improve performance for those using graphical effects and more. The Unvanquished engine's renderer was originally derived from XreaL while now it's evolved into a radically different beast. Both the new and old renderer will be around for a few more releases as the new tile-based renderer doesn't yet support shadows and some other features, plus there is always the chance of regressions.
Unvanquished Alpha 49 also brings some new models and other in-game improvements. More details on Unvanquished Alpha 49 and the exciting rendering work can be found via Unvanquished.net.