After and exhausting process I've narrowed our search for replacement windows down to two... the Viewpoint (by Norandex)3000 series, or the Serious Materials 301. Does anyone have any expertise to offer on comparing these two products?

Hi Junemommy, when choosing replacement windows it is important to consider both your design goals and where you live. The 301 Series from Serious Materials is an excellent product and will meet ENERGY STAR requirements in all climate zones with its standard glass packages. Taking a quick look at the Viewpoint 3000 I don't see their performance data readily available on their website, but I do notice that low-E glass and argon fills (two key elements for ensuring high thermal performance) are "custom" options - they don't come standard. That is something to think about if you want to get the $200 tax rebate from the federal government. The 301 Series features the best in glazing technology, it is powered by SeriousGlass, the same product used in the retrofit of the Empire State Building. Hope this is helpful!