It's not really a apples to apples comparison. The STW has a considerable case capacity advantage over the new 7 PRC.
The 7 STW, 28 Nosler, 7-300Wby and 7-300PRC all have nearly the same case capacity (95-98gr H2O) so that's a better comparison.
If you're thinking the new 7PRC is just a necked down 300 PRC, it isn't. The new 7PRC is a much shorter version of the 300 PRC case and has considerably less case capacity.
The new 7 PRC, 7mm Rem mag, 7 WSM, and 7 Blaser mag all have nearly the same case capacity (80-84gr H2O) so they're a better comparison to one another.