The 5100 is the same radius as the Radius 1 or 360mm. This is essentially the minimum radius of almost all modern Marklin rolling stock but may not look prototypical. (Edit: I originally thought the 5200 was R1)

However most other brands need a larger minimum. I am not sure about Brawa but most North American rolling stock will not work on anything less than Radius 3 515 mm (20") as most NA manufactures have an 18" (457mm) minimum for era 4-6 rolling stock.

I am planning my mainline with minimum radius 3 and using wide radius turnouts.
I can use the radius 2 switches for yard switches as the sharp curve is short but will only use yard speeds.

I will be using the R1 and R2 curves for branch lines.
Most of the era 1-3 locs and cars were shorter and would look fine with the smaller radius.

Edited by user 13 October 2012 03:15:17(UTC)  | Reason: Wrong M track P#

Correct!