E6500 vs E6510 construction.

I'm looking to replace my long serving Latitude D620. I was heading in the direction of the E6510 until I came across some refurbished E6500's on the outlet site. Looking at the specs it seems to me that the E6500 is almost entirely made from Magnesium alloy while the newer E6510 appears to be made using a "Tri-Metal" frame covered in plastic. This seems to me to be a backward step - can anyone who has owned both models give me some information on this? It is hard to get accurate information from Dell's site and there is a lot of conflicting information out there.

Which model seems tougher?

What exactly is "Tri-Metal"



I reckon the earlier model looks better, it's also 16:10 rather than 16:9, which is good I think. As far as performance goes either one would be a big step up from what I am using at the moment but mostly I just hate plastic!