Melodyne should not stress computer cpu unless it is on its last legs and up for replacement

Not clear if you are talking about melodyne editor or single tracks - big difference.

I abandoned Realtracks for too long because I found it buggy but I suggest you check out realband tips and tricks and update to version 8 which is stable in windows.

There is a lovely section on regenerating sections of your song until you get the version you like in realband tips and tricks in support videos

Much much much quicker than exporting to melodyne unless you wish to change the dynamic and music content