I'd go with the E5-1650 and if possible put in more ram onto the box and have it load more from the ram. Also as others said make sure you get an SSD for this it will bump performance up a huge amount.
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Lots of ram is nice for caching but if the server reboots the performance can take a hit while everything get's cached again unless you run an automated cron to stuff the things back into a ramdisk after a reboot. Personally depending what disks you have currently I would be looking to upgrade them first as generally poor I/O will increase CPU load anyway. Make sure your caching what you can that includes the database as ram is faster than any disk even these all singing SSD's which are being talked about all over the show.
How big is the database? You might be able to load it right from your memory which would insanely speed things up for you. If not, use SSD's as that also will offer a huge performance increase if you are not using them already.