Providence is approximately the same distance as Worcester, and Mansfield about the same (3 miles further) as Framingham. With the current schedule, AM peak travel times to South Station are:
Worcester: 99, 88, 102, 75, 99, 93
Providence: 73, 75, 72, 72, 64, 76, 77
Framingham: 55, 44, 58, 33, 55, 44, 55, 50, 55
Mansfield: 44, 45, 41, 41, 41, 32, 46, 48
So the Providence Line is already reaping the benefits of fast track speed and wide station spacing, with massive ridership (1000 to 2000+ riders per day) at every station from Route 128 to Providence. The Worcester Line has higher population density and arguably a worse highway (with few local exits); there is a massive ridership potential that faster and more reliable service can and will unlock.