why you care about 64 bit ?
I dont think Pharo is 64 bit ready but it should be soon
The big advantage that 64 bit gives is more memory access , 32 bit has access to 2 GBs of memory. Even in memory its not such a big deal because you can launch multiple instances of pharo and take advantage of your entire memory , the advantage also doing like this�� is that will give you the ability to run pharo on multiple cores something that a 64 bit VM by itself cannot do anyway, pharo / python / ruby etc.
Lack of 64 bit is definetly not a good reason not to use pharo, there are good reasons not to use pharo, but this one is not one of them.