how are these 6 cyl motors?

You won’t win many drag races... but they are adequate for normal driving.
One of the best ever built for durability.
For instance there is no real interval for replacing the timing chain.

__________________
-Marty

1986 300E 220,000 miles+ transmission impossible
(Now waiting under a bridge in order to become one)

Reading your M103 duty cycle:
http://www.peachparts.com/shopforum/831799-post13.html
http://www.peachparts.com/shopforum/831807-post14.html

in the 's' class cars and the 'e' class?

Yes.
http://catalog.eautopartscatalog.com/mercedesshop/sophio/model.jsp?header=header.jsp&footer=&partner=mercedesshop&baseurl=http://catalog.peachparts.com/&year=1990&make=MB&clientid=catalog.mercedesshop&cookieid=1FX0MB1RS1J10ZTXG9

__________________
-Marty

1986 300E 220,000 miles+ transmission impossible
(Now waiting under a bridge in order to become one)

Reading your M103 duty cycle:
http://www.peachparts.com/shopforum/831799-post13.html
http://www.peachparts.com/shopforum/831807-post14.html

Not what I'd call economical if you run with the top 25% of traffic. My 91 300SE netted 17 city/19 hwy while the S420 gets 16 city/20 hwy. I prefer the car that can keep up with an ES300 when necessary.

That engine is more balanced in a 300E, that body is more balanced with a V8.

Working on that engine is like shooting fish in a barrel.

Sixto
95 S420
87 300SDL

They burn oil, also a little to much car for that engine. If you are going with a gas car just get the biggest engine availible. All gas W126's get poor mileage might as well have a big V8 to enjoy while you are feeding it.

__________________
1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200