I think this depends on the degree of service and, most importantly, the access to the audience who'll buy these records. I would pay more to someone who has a track record of selling the best records for the highest prices. It also depends on the broker's ability to collect consumer information to use for future sales. You should be able to negotiate lower if the broker has the ability to own the buyer's contact information afterwards for their exclusive use. That also assumes though that these records are what you say and will command significant attention. I actually think selling piecemeal rarely justifies the money earned. I would recommend trying to find a broker who's able to find a buyer for the entire lot at a fair price.
Another alternative are renowned record stores themselves. Many of the best record stores (including those on eBay like carolinasoul) source records internationally and have buyers stationed regionally to scoop the best products at the fairest prices. These stores will often pay upwards to 70% of discogs value on the records. To me, that's good value for a seller looking to offload records in bulk. I would personally go this route first especially if you're looking to sell by genre. What you wouild need to have done to benefit from this is to price the collection according to discogs market rates and have those figures ready when approaching stores. I would, however, determine first and foremost who the major players are in terms of selling the type of vinyl you have.