Well it's actually not faster, or it could be faster........ it's different. Also you've only posted the processor speed, not the buss speed, cache size ect. Raw ghz mean less than the potentional bottlenecks on your system when the specs are that close.
You switched from an AMD processor to a Intel processor. They are totally different animals.
Things you should check:
Make sure your mame settings are the same.... they make a difference!
If they are the same try changing them, again they make a difference.
Make sure you aren't running a build of mame optimized of amd processors, you are running intel now.
Defrag your harddrive..... I dunno how it could be fragged after a format, but if you did one of those cheapo "quick formats" I guess it's possible.