I was buying parts for my 1972 300sel 4.5 when one of the mechanics said: "I believe if I were going to put up with all of the air suspension headaches I would buy a 6.3". Another customer then replied: "I believe if I were going to put up with all of the 6.3 headaches I would have to buy the 600". I drove a 6.3 before I bought my 4.5 and the 6.3 is an incredible engine. The biggest difference is the 6.3 was quicker off the line. At 65,70,75 mph the 4.5, when you "floor it", takes off like a rocket. At 80+, everything about my 4.5 starts making sense. The 3.5 and 4.5 are 230h.p. The 3.5 has a higher compression ratio, The 4.5 has more effortless torque. The lowest production V/8 109 car is the 4.5. I chose the 4.5 because I liked the condition and it had more options than the particular 6.3 I was looking at and the fact that the 6.3 is a bit more prone to overheating. The top speed of all 3 V/8's are very close to one another. If it is the design of the 108/109 you like then a 280sel 4.5 is probably more user friendly. Don't under estimate the big sixes either.

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"BECAUSE KNOWING IS HALF THE BATTLE"
G. I. JOE.