The Topre has a much softer feel and is not as clicky as the MX Blue.
I think the blue is also a 55grams switch (confirmation required by a Geekhack expert)
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The actuation seams higher on the Topre. Also the key travel on the Topre is smoother. It is a very quiet board. It feels a bit less tactile than the MX blue.
Two different animals.
The Cherry MX Blue key switches require less than 55g of force. The Wiki may have the exact specifications.
I'd be interested in you feedback after you've had the chance to type on your 55g 87U for a while. I have the 87U with variable weighting and enjoy typing on it for hours on end. A 55g keyboard without mechanical clicky key switches seems like it would feel stiff after a while, but perhaps your experience will be different.
Edit: The Wiki lists the Cherry MX Blue key switches as requiring 50g. I haven't measured the required force but my Blue Cherry Filcos seem lighter than 50g. It might be time to pull out the ripometer to see if the ligher key presses on the Filco are just an illusion.