But you think it's worth the $120 upgrade, seeing as you have him buying a new mobo AND a new HSF. So for an extra 15 bucks, he could get a better CPU, and a board with more upgrade options since it will support the newer AM3 chipset. He'll still be able to overclock to 3ghz+ on a stock HSF.
Also, you say the E1400 is the same as your E2180? Even against the 7750, it fails at stock speeds. Not to say that you couldn't overclock, but you can also overclock the 7750, so it's really a moot point. And this way he doesn't need to overclock.
AnandTech Bench (beta): AMD Athlon X2 7750 vs Intel Pentium Dual Core E2180