If you purchase a crossgrade it is less likely the same drivers will be used. Thus no conflicts.
This means both can co-exist without the need for either to be aware of the other.
And it is likely w2 will be quicker. But will require a break-in period, and a few service packs, to assure maximum performance.
The extra hardware (house/apartment,...), and multitasking/timeslice allocation on your part, may prove expensive and exhausting.
But, uninstalling w1.634 may result in never ending support requests.
So the decision to simultaneously use both may be the best way to go.