Tas, welcome to Sevenforums!
There is not really any benefit to using 64 bit ultimate if you only use 4GB of RAM.
64 bit enables you to use more than 4GB of RAM, so unless you are planning on increasing the RAM, it is probably not recommended. You gain no speed from it in and of itself, and if anything it is slower than 32 bit ultimate with less than 4GB of RAM. But if once again, if you are planning to increase RAM, you will notice faster speeds with the 64 bit ultimate installed. However, you will need to completely reinstall the ultimate software and lose all your installed programs.