Depends really. You need to ride a DH bike quite hard to benefit from it.
I race a 150mm 29er for the odd DH race. Much to the annoyance of the other guys, I nearly always podium, beating a bunch of people on DH bikes. It would probably be a different story down some super rough, steep & long tracks, but who knows until you give it a crack. It would take me a while to get back up to speed on a DH bike again, having not ridden one for a while.
The limiting factor is generally the pink blob on top, rather than the bike. One of the guys I used to race with would regularly beat 75% of the field on a hardtail, at big races too (Dragons/Pearce/etc) so proper tracks as well. You bike will generally go a lot faster than you.