Also look in My Computer for the exact model number of your i7 - it should say something like "i7 3840QM".
http://www.cpubenchmark.net/singleThread.html shows the fastest i7 to be 2.75 times as fast as the slowest, so it makes a difference.
However, from your description of sudden 'chokes' I suspect memory is the most likely issue, or possibly a 32bit limitation as Doug says.