any/all XMOS apps plus any other area where extra speed would be required i.e 3D rendering, video applications etc.
also running old 68k apps/games with E-UAE (with integrated solutions like glUAE or RunInUAE) would drastically benefit from the extra speed
Which XMOS Application? There's none.
But extra cpu power is always welcome, for browsing, video, raytracing, compiling, UAE whatever. The more the better. But question remains: for what price. And taking the price into account the X1000... Well, it's up to each one¹ to either rob a bank, sell your stocks or take a mortage on the house.
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¹ My answers to those questions: wouldn't tell here/keep them/get real.