Most multi-core games use 3 cores. The ones that use more don't benefit by more than a few frames.
Even then, most games use 1-2 cores. The E8400 is going to be faster per clock/core while having similar (or better) max OC capabilities, however you may get slightly better performance with the 955 BE in multi-core games.
Here is a nearly clock for clock comparison, these CPUs will OC to similar clocks (the E8400 tends to do a little better; 50-200mhz).
http://www.anandtech.com/bench/Product/55?vs=88
What is the point of this question? The E8400 is quite out dated and isn't sold (new) at reasonable prices when building an entirely new system.
In the majority of games I'd hand it to the E8400 with the Phenom II not far behind. However yes, more and more games are becoming multi-core and slowly showing more benefit.