32 vs 64

In MBP I could boot to use the 64 bit kernel from this I have to check if firmware supports it by entering below in Terminal

ioreg -l -p IODeviceTree | grep firmware-abi

If the return is 'EFI64' then I just need to boot by pressing the '6' and '4' keys together while starting up.

After trying Windows 7 x64 bit with Office 2010 x64 bit public beta I just couldn't see much difference in performance. There is also printer driver support problem if I run Windows 7 x64 in the office. However it looks like that memory utilization is slightly better in OS X running 64 bit.

Now if you want to boot into x64 all the time you could modify this file

/Library/Preferences/SystemConfiguration/com.apple.Boot.plist

to insert this between 'string' tags

arch=x86_64

Before you do the above first of all you'll need to gain root privilege into your MBP. Haven't done this before here's the way.