hardware advice

Hi everyone,

I want to buy a new server, and am contemplating a Dell R710 or the
newer R720. The R710 has the x5600 series CPU, while the R720 has the
newer E5-2600 series CPU.

At this point I'm dealing with a fairly small database of 8 to 9 GB.
The server will be dedicated to Postgres and a C++ based middle tier.
The longest operations right now is loading the item list (80,000 items)
and checking On Hand for an item. The item list does a sum for each
item to get OH. The database design is out of my control. The on_hand
lookup table currently has 3 million rows after 4 years of data.

My main question is: Will a E5-2660 perform faster than a X5690? I'm
leaning to clock speeds because I know doing the sum of those rows is
CPU intensive, but have not done extensive research to see if the newer
CPUs will outperform the x5690 per clock cycle. Overall the current CPU
is hardly busy (after 1 min) - load average: 0.81, 0.46, 0.30, with %
never exceeding 50%, but the speed increase is something I'm ready to
pay for if it will actually be noticeably faster.

I'm comparing the E5-2660 rather than the 2690 because of price.

For both servers I'd have at least 32GB Ram and 4 Hard Drives in raid 10.

Best regards,
Mark