As to my expririence – it can be very different for vendors.
Ericsson recommended signallink link load – up to 40%, but Huawei says that they supports up to 100% signalling link load without any problems.
That’s why number of circuits can be different.
Also, please, mension, that better to specify which signalling protocol are you using for that signalling link? Is it ISUP, R2, QSIG or PRI signalling…