The Honda more closely resembles the C250. The silhouette is very similar.
My gf has the 250 coupe and I can tell you that the turbo charged 4 cylinder has much more "zip" to it than the V6 in either of my E350s. The 2014 E350 is faster than the 2012. But her 2012 C250 is faster still. You won't have a problem being the first one out of the gate at a red light. The 250 is lighter overall, but still the extra weight of the E350 should not be a factor with the bigger more powerful engine.
Now on the interstate, it is a different story. But her 250 can still hit 90mph without a second thought or breaking a sweat and still have a lot left in the bag in case you want to punch the pedal.
I believe it was the Honda Accord coupe that came out before the current Mercedes C class coupe.
the E350 has the M272 V6 engine which has 268 hp/258 tq. Now, unless you have the M276 engine with 302 hp. I don't think the C250 was sold in the US, I think that we got 300s and 350s. If your gf C250 is a coupe, then it is carrying a lot less weight and is more balanced than a E350...also depends if it a standard one, or with 4Matic as well, or with sport paddles.
Lighter weight can trump extra hp...Colin Chapman was about Lighter weight, that is what made his Lotus' so good.