I have to say if you are looking for reliability, the 996 Turbo, GT2 and GT3 engines are very reliable - they are based on a 993/964 block (early ones had this 964 stamped on them even) and were developed for the GT1 - a proper race engine.

If you have a warranty from porsche I would not worry - but if you plan to track at all the GT1 derived engine can stand up to a bit more abuse!