Personally I wouldn't go over stock any more :S +0.1 over (so 2.2v) should be fine, +0.2 would decrease life expectancy moderatly - depending on the chips anything down to as little as 2 years, +0.3 you can expect random failure - they might last 3 years fine or they might only last 2 months.
Conventional wisdom puts +0.1 on top of my figures - but this is my experience from several different lots of DDR2 memory over quite awhile...