Apple Computer Inc will come out with a six-slot model in its NuBus-based Macintosh II family to be based on the 50MHz version of the 68030 early in 1990, says to Macweek magazine. The new IIxi will be 30% to 100% faster than the current top-of-the-line IIci, the magazine hears; it is expected to be accompanied by the introduction of the 7.0 release of the operating system.