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
to insert this between 'string' tags
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.