Does it matter its slower @ startup? Yes 64 needs some more memory for example if u got 2GB @ 32bit u need 4GB @ 64 bit. But this is worth it especially for something like Java. Start up is irrelevant when the server is more online then starting up ( atleast i hope for you ).so java on 64 bit is slower then 32 ony at startup?! kinda unclear..., might that be the reason of fluctuation..
afaik adressing in 64bit memory is more effecient then in 32bit. But because it contains 64bit and 32bit information for adressing its abit bigger. Having all parts (cpu, os, software) 64bit should improve the usage of java i think.
Ill be confguring my server soon maybe ill do a small test 32bit versus 64 bit. Could be interesting.
As for the Thread pool values im very interested in. maybe nBd could explain or give us a source of your recommedation to make the values the same as core count?