Here is what I feel will happens roughly :

if (JRprice == x)
{
     masterXchangePrice = x - 10%;
}

In my humble opinion, trading OTC will impact the market more than trading quietly on an exchange.

First, all trades impact the quantities available in the same way, if you sell 1000 MSC OTC, that will always be 1000 MSC that wont be bought on the market. There is no "if you dont trade on the exchange the price will not be impacted !".
Thats an economical fallacy; the price converges to the same value everywhere and the exchange is a part of the market in the same way that the OTC is.

Second, saying that you have X quantities to sell at Y prices is much worse than trading them little by little : As long as the market expect a bigger quantity to be traded, the price will correct itself until the price discovery process is finished. Thats like bill gates announcing that he will sell 1% of MSFT the next week. What huge holders are doing is that they pay brokers to liquidate the quantities as quietly as possible on the marketplaces.

Having said all that, I will add that this is only an opinion and that its really great that JR is commiting himself to Mastercoin full time

This is all fascinating to follow in term of economic theory