The compromises and cost of increasing to speed from 100 to 110 are far less than from increasing the speed from 110 to 125, so you don't need to have an much running at 110 to merit the upgrade – and it will be a boost that all trains running can benefit from, unlike the putative increase to 125.
With modern ac motors and electronic control systems, there is not really the old big compromise between acceleration and top speed from dc motors.
However UK has safety rules about extended nose and crash zones, which also prevent passengers using outer part of the end coach for stock above 110mph. So losing this space is only justified if can do sustained running at higher speed.
The Transpennine units will be 121m long. Although power hasn't yet been announced, the Stream units being built for Italy are 2.06MW for 66m long ETR103 and 84m long ETR104. The regional version ETR108 is 165m and has 4.12MW (also has a higher 200km/h top speed). Therefore I am guessing the 121m UK version will be about 3MW (about 4000 HP). The now superseded Aventra is about 2.3MW for class 720, 730
Journey time isn't really going to be determined by saving few seconds per mile at 90-110mph, it will be slow approaches to junctions requiring crawling at 20-40mph that takes a whole minute rather than passing through in 15-20 seconds