The test ride is the main test for you. I have a good CF and I have top rate Aluminium. Not the run of the mill stuff used on most bikes. IF I have a choice -I ride the aluminium. The ride suits me better as it is more lenient on the body but that is down to my style of riding and the materials used. Test ride to see if you like the Roubaix.
On weight- 6 lbs is a lot but what you may not notice is the difference in groupsets and the quality of the wheels.
But that offer of trade up is good. Proividing you can feel the difference in the bikes----------------------go for it.
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How long was I in the army? Five foot seven.
Spike Milligan