I find more problems with the GUI and Java concerning Macs than Windows in this forum, although I assume that there are much more Matlab sessions running on Windows platforms. Let's ask some Mac users, if Matlab is stable enough for a dayily work.
"50 million rows" might be a tiny or a huge problem: It depends on how long the rows are. a [50 x 1] double vector is easy to handle with a 2GB RAM machine.
If more cores or a higher CPU frequency is more useful depends on your code: If it is parallelized or multi-threaded efficiently, more cores can be the better choice. If not, than a 6 core CPU might outperform your very expensive computer easily.
That the frequency is lower if the number of cores increases, has simple physical reasons: heat.
