Yeah, Win7 is really good. I understand misgivings updating from XP, but thier really is no downside to the upgrade. Win7 is the new XP
Assuming you dont pirate it, there is ...... Win 7 costs money. And for what it does cost, there is little you get for that money, as most functionality that is actually better in 7 than in XP can be easily upgraded to XP free of charge. IDK what Win 7 cost ATM, but I doubt it is cheap enough to justify its price tag.
Windows 7 accesses and manages a lot more memory in an efficient manner for sure.
True - for the 64 Bit version.
As you need 64 Bit support for what you are doing, there is however NO point at all in getting Win XP 64 Bit. As it has been mentioned before, XP64 has suffered from poor support from the beginning....
If you need 64 Bit now... go for Win7 64
Considering how terrible Win 8 is (I played arround with the preview version) buying a - not locked to the machine version - of Windows 7 now might actually not be a bad idea...