The RS3 has more power and revs higher. I only have one liter through after break-in and race tune, but initial observations are that there is much more low end (I have to be very gentle out of corners), similar or a little less mid and then tons more top end. The RS3 is uses more fuel but is easier to tune and idles better than the GT3C.

The revs are so much higher can gear lower and ORCAN recommends changing the conrod and wrist pin after 3 liters on large tracks and 5 liters on small tracks! The engine uses the 7601 rod which has never been a long life rod.

Even though I am notoriously greedy when it comes to power the RS3 could have too much power and torque for some people. I am tempted to say it is too powerful for my taste, but I am still experimenting with ways to get more traction/less wheel spin and tuning the engine to make it more mellow.

You should try for yourself as the RS3 is a beast!! I need more time to say for sure. I love the GT3C and it has really served me well. I need more time to either get used to or figure how to better handle the RS3. My buddies are going to give it a try soon and we will see what their reaction is.