The 300D turbo and 300SD through 85 will top out at 105-115 mph. 140kph all day long is not a problem for these cars.

The 300D turbo and 300SD through 85 share an engine. Minor differences from year to year but the same within years. The 126 is no less reliable than the 123. The 126 has motorized seat adjustment and a dedicated electric central locking pump but these devices have proven to be solid in cars with over 300K miles. YMMV. It boils down to preference.

For $6000 you should be able to find a nice 87 300D or TD (124s) or an 86-87 300SDL (126). The 6 cyl turbo allow these cars to top out around 120 mph and it doesn't take long to get to that speed.

The 124 went on to have a 5 cyl turbo in the 90-93 300D 2.5 (not the same as the 7x-85 5 cyl) and a 6 cyl 4 valve NA engine in 95 E300. If you find a 90-up 124 Diesel in SoCal for $6000, run away from it.

The engine in the 95 E300 carried over in the newer body style 96-99 E300 (210) gaining a turbo for 98-99. If a chipped Jetta TDI is your benchmark, try a 98-99 E300.

The 126 went on to have a bigger 6 cyl turbo in the 90-91 350SD/SDL. Stay away from $6000 examples of these cars as well. In fact do a lot of research before investing in any 3.5l MB Diesel.

The 3.5l Diesel continued in the 92-95 300SD/S350. Fabulous cars if you like to travel in a living room (as I do). They might not be the most reliable MBs but you can keep your Jetta in the trunk

Sixto
95 S420
87 300SDL