I'd try to find a 420/560SEL, I've had a few and could never live with a 300SE/SEL. I've been shopping for another 126 for at least 6 months and I don't really see much savings in purchasing a 300SE/SEL rather than a 420SEL or 560SEL, so what's the point? Gas savings?? Maybe when the cars were newer, the V8's commanded a more noticable premium.
Also, I'm pretty sure 300SEL's are rare, most of the 300's produced were 300SE's (I think).
2003 S500 Black/Charcoal
1990 560SEL 61k Arctic White/Grey
1988 420SEL Black/Palomino Sold @ 85k
1987 420SEL Midnight Blue/Grey
1986 420SEL Diamond Blue/Grey
1983 380SEL Champagne/Palomino