Back in the late 1960s a local fellow (central VA) had an R4-equipped '63 Avanti. The car went through several owners, and by the time the engine failed, ALL the rings were broken and two cylinders were ruined. Sunoco 260 was the only gasoline adequate for a 12.5 C.R. and not all of those owners knew (or cared) that the engine had to have a very high octane gas.
But, to answer the original question, an R4 should beat an R3 to about 25 MPH, just as an R1 will beat an R2 to 25. The reasons are obvious. Above 25 the R3 will reel in the R4 pretty quickly, especially if the R3 has high output pulleys.
--Dwight