The E8400 was pretty much the most powerful Core 2 Duo on the market before the Core 2 series was phased out. That being said theres not many mobile CPUs that come close to it. If you want a laptop with a CPU that came close look for one with the i5-4310M or i5-4340M. Those CPUs would be the closest to what you specified.
The i7 CPUs in laptops are more closer to the Core 2 Quads.
Also avoid any CPU with the letter U at the end.