Should not be that hard to achieve 1000fps in the 10mm with a 200gr. bullet with careful loading. I have some of the original Norma 10mm loadings. The 200gr has a velocity of 1200fps and the 170gr HP has 1300fps. I have shot these (though limited times) in my Colt Delta Gold Cup. I believe these original loadings by Norma were for the Bren Ten.
Handgunner