Unless you are doing so much LR/PS work professionally that any time savings there are really important, then I would consider the whole system.
That is .... will changing platforms make your entire computing experience more or less efficient. There is no point in changing to a PC to save 30 minutes a day (a lot!) with LR/PS if you spend 45 minutes extra per day doing other things.
On the other hand, if you are spending 20 minutes a day booting back to Boot Camp partition (and back to OS X) because OS X is missing something you need, then there is no point sticking with a Mac just for LR/PS.
Of course, if you are talking about installing OS X on a hackintosh, then that is another discussion altogether. Though the principles still apply... if the hackintosh takes up more admin time than the PS/LR savings....