Peco SL-200 flex is 24" (609mm) long. It's as easy to look up as it is to speculate: http://www.peco-uk.com/product.asp?strParents=3309,3310&CAT_ID=3314&P_ID=17078 (Sorry, Jeff, but it's hardly "near absolutely identical" to Märklin's flex.)
Sorry David I tried to quick look up "Peco SL-200" and got not nothing other an retailers or forums, NOT peco's site. Did see a 24" reference so assumed some 660mm rounding. Never measured it as flex always gets cut off. But, besides the ties (sleepers) being about .015" longer, you would be hard pressed to tell which is which when placed side by side. The rail, tie plates, tie 'wood' grain, etc. Same when first looked at it. Liked the wet noodle flexing ability but prefered the significantly better look of MTL flex, even if at half the length.
I just Googled "Peco SL-200" now. Peco's site came up as the 7th link in the first page. Are you not using Google? Interesting. I have some of each, and I find the two brands to be as different as night and day. The shape of the ties, the rail profile, how the rails are attached to the ties--they look obvious (to me) that they are different products... I guess we each have our different perceptions.
I did some masurements some years ago. You can find it here: http://www.platelayer.com/z-scale-track-dimensions.aspx I have used all 3 types for many years and there are some differences, specially when you are working with them. The easiest to lay is the Peco track, its very easy to have smooth curves, but it will not stand in the position. MTL is a little more difficult to have 100% straight, because it holds the curvature when you bend it, which I really like. Märklin is very similar to Peco to use. The look of the tracks are a little different, if you are running American prototype, the MTL track looks best, with more correct spacing between the ties. I use MTL in visible areas and Peco or Märklin mainly in hidden areas. The track-string hight profiles are not 100% equal, but its easy to mix the brands, they work well together. I also like to solder the track, it gives you good electrical contact and a more stabile track. Here is some work from last night, playing with all types, MTL, Peco and Märklin: http://www.platelayer.com/finally-all-tracks-are-installed.aspx This is some of my experiences after laying 100's of feet of Z-track during the years.
