Two 10Ks would be awesome over a 75. I don't think that would be too much light at all, even at 8-10". The 250 Saki's you had would be close to the par of a 400 10K I bet, but I could be wrong. I havent seen the numbers of a 400 XM, just bulbs like Aqualine Busche and the like.

Be sure to leave the glass in those pendants (if you are using them), it will help lower the amount of heat they give off tremendously.