That's not a Core 2 Duo so to compare this we'll really need to benchmark the final machine. Is whoever is piecing this together able to let you get a benchmark like you find on Tomshardware.com?
I'm building a new pc and am naturally inclined towards intel. BUT I can get an AMD processor + motherboard for a good 50~100 $'s cheaper. Wil it make any real difference in gaming?
the x2 5400 should be around $80 (US$) while the e5200 should be about $85. motherboards for either start at $60 or more.
the e5200 will be faster than x2 5400+ since it trades blows with the x2 6000+. http://www.xbitlabs.com/articles/cpu/display/core2duo-e7300-pdc-e5200_6.html#sect0