I'm thinking of doing the same. Nowhere have they officially informed me what the transfer rate to Marriott points will be, and the rate in the MR portal still says 1000MR:500SPG. I only have 40,000 MR points and don't want to keep the card, plus it isn't much use in any of the other programs, really what is the risk with trying and then making a complaint should the points come through at 3:2.
My advice is take the screen shot with the ratio it shows currently, and put the time log into it, and meanwhile also put the time log when you do the transfer, just in case if something goes funny afterwards.