The Barracuda Green 2TB is an attempt by Seagate to crack the low power consumption and excellent acoustics of low power desktop drives from WD and Samsung. The Momentus 750GB on the other hand doesn't have much to prove, coming from the same stock as the surprisingly quiet Momentus 7200.4 and XT.
Any major computer upgrade generally requires a full software reinstall too. No so if you heed the advice in the guide to Upgrading a Motherboard without Reinstalling. PCSTATS Tips