3 stick of ddr333 = stabilty problems?

I'm thinking of adding another stick of 512mb pc2700 ram to my system since prices are so cheap. The only problem would be that all three slots would be occupied and my MB only supports 2 in ddr333 mode. Has anybody here tried using 3 sticks of pc2700 on a kt400 MB? Did yah encouter any stability problems? Maybe I should just run @ pc2100 speed and not worry about it.