Well, since I'm probably the only member with both boards, I guess I'd be qualified to answer

The Topre is definitely lighter. However, as it's tactile, the subjective weight is fairly close.
If you tend to bottom out, then the Topre will quieter, as the MX Reds tend to "clack" and the Realforce, "thock".
Given the choice between the MX Reds and Topre 30g, given how prices are atm, I'd choose the Topre. However, if you can find an MX Red board for under $100 (I've seen them as low as $45 new, but that's unlikely to happen again) then it would be my first choice.