Minecraft Freezing and Pausing.

I have seen a lot of threads on this forum and others where people say that they get pausing and freezing when playing Minecraft and like others I am experiencing this too and I have a fairly powerful PC. I can play World of Warcraft with quite high graphics settings however I have noticed a few things. It will only happen when using textures above 16x16, The one I am using (but I have tried others too) are 64x64. When using the vanilla texture it is Ok. (im using MC 1.3.2)

I have also found that it is sometimes the world as I can use one world with the texture pack Ok but a new world I create would experience problems but when it freezes I can not even press the ESC to get back to the menu, not until there is a few seconds of unfreeze again and then I can click ESC but then even in the menu it would still freeze.

I have used OptiFineHD and that did not fix, I have used McPatcher and that did not fix it too. I have noticed in McPatcher there is a memory setting, I think default set to 768, I am going to try and see if by noticing that up a bit would help. I am not new to programming as I do that as part of my job but I am new to JAVA but I do know that JAVA can be iffy at the best of times.

Has anyone else come across this before and fixed it with ease. Is it to do with the memory allocation settings?

Thanks
C.