If you're even remotely tempted you should get SH3 again.
Factor in five years of community mods and development and you still have a great game which stands up well as both a simulation and a game today.
Silent Hunter 3 with something like the GWX mod is the natural competition for Silent Hunter 5 and is the reason why everyone has such high expectations of the new game. Unfortunately it is also the reason why a lot of people might be disappointed with SH5 - all the work people have put into making mods, additional content and improving the historical accuracy of SH3 is honestly more than any retail game can expect to live up to at present.
Let's face it though, there is nothing stopping you getting both - SH5 for the eye candy and SH3 for the realism.
