I won't by any means upgrade or change my PC until SH5 is released, all patches that have to come made available, and a year has passed by. That's the best giarantee that I will find for a reasonable amount of money a PC that lets me enjoy the game and even scratch the best of it.
I did it with SH4, which stuttered a bit in my good-enough-for-SH3 PC, which currently runs SH4 and SH3 in a breeze, and I will do the same with Sh5. Let it stutter a bit in the beginning and shine later for reasonable budget