We've checked in 7pcs (allowance was 6), SFO-xHKG-SIN, twice, without an issue. The 7th piece was a standard carryon that we could have taken to the cabin along with our small backpacks in any case..

The first time, we were probably over the 6*32 kg limit (stuff while setting up home in SIN), but well under, the other time. CX SFO staff do have a reputation for being nice and helpful, but it could have something to do with them being nice to MPC elites (DM and GO, on paid biz tickets, and I had an opup to F the first time, while both were 'birthday upgraded' to F on the second instance).

I'd say be ready to payup- it's not too much as compared to what some other airlines charge, but do request nicely.