First, I do not know your market. (disclaimer). You may not be aware that fees vary from area to area, so I would be surprised if you actually receive a pat "I like proposal A!".
I am assuming that your goal is to maximize your profit when you sell, right? Califl. Association of Realtor Buyer survey shows that 90% of the time, the buyer sees the home they purchase with a Realtor, so you definitely need to attract Realtors, who most of the time have the buyers.
You may be unaware that Realtors sign a Code of Ethidcs when they join the National Associaiton of Realtors. Part of the Code prohibits us from "steering" clients. That means that if there was ONLY an above-average commission, that alone will not cause a Realtor to show a property. However, combine above-market commission with a well-prepared property offer our clients value, then you have a pretty powerful combination.
So far as the "sliding scale" approach goes, there are two sides to your idea. One is that, for listing agent, technically I think you could offer them an incentive. However, There may be ethics questions regarding compensating the lisitng agent for a higher price based on the MLS rules. (everyone in the Realtor community wants a level playing field).
However, for you, this is a one or two time project, selling your home. For us, buying and selling homes is our livihood. In most cases the fee negotiated by the seller and listing agent is split equally between the listing office and the selling office. If word gets out that the split is not equal (this is called a variable commission rate, which also applies to other arrangements), it can create bad relationships between Realtors.
In the sale of a property the first part is to attract a buyer's agnet, then a buyer, then a lender who will fund the loan, then a appraiser that will certify that the property is worth the sales price. Given the current market conditions you can imagine that lenders are anxious about making a loan for more than a property is worth.
So I hate to upset your theory, however the truth is that the market sets the price. Once an offer is accepted, it's BOTH Realtors' job to get the process through escrow. In truth, this is where we earn our money. Anyone can put a property in escrow, it's closing that takes skill. i
I do know a little about the Southern California market, and IMHO you need to find a Realtor that has a firm grasp of the market conditions and what it will take to sell yoiur home for top dollar. My studies repeatedly show that homes that sell in the first 30 days sell closest to list price. So the longer the property is on the market, the larger the difference between list price and sales price. For the month of November the MLS shows that wthin 30 days homes sold at 99.4% of list price. 120 days, 94.6%..remember that the list price at 120 days has probably been reduced at least once or twice.
Hope this is not too complicated.