Anyone here have a .502 Thunder Sabre from Big Bore Canyon?

How does it compare to the .499, .50 Beowolf, .458 SOCCOM?

The 502TS is essentially a 50AE with a 7.62 x 39 bolt.  While it makes sense from a manufacturing point of view (off the shelf bolts) it turned out that it did not allow what the originators had hoped for.  The large rim of the 50AE limits the max pressure to which you can operate the cartridge before lug failure occurs.  By going with the smaller rim on the TS they hoped to be able to go with higher pressure and increase performance.  They found out however, that the brass would collapse upon itself.  Thus, they are left with essentially the 50AE with a smaller rim.  It still allows use of the off the shelf bolts, but offers no real advantage over the 50AE.

As to comparison to the 50B, 499LW and 458S, all of those have longer cases (1.5ish compared to the 1.3ish of the 50AE/502TS) and will outperform the 502TS.