I'm of the opinion that the fast Corby services will need to be operated by 110mph stock to fit it into fast line diagrams on the MML.
My opinion is different.
In the peak, when capacity is tightest, all EMT Corby services have pathing time in between St P and Bedford to fit them in with the Thameslink service on the fast lines. Therefore operating at 100mph will actually help the timetable work better, without loss of journey time.
North of Bedford, it is 15 miles from Bedford to Wellingboro' and only 5 miles from Wellingboro' to Kettering South Jn. Trains will be above 100mph for perhaps 10 miles of the former stretch, and little if any of the latter. The difference between 100mph and 110mph is 3 seconds a mile. Therefore with the same rolling stock, a 100mph train calling at Wellingboro' and Kettering (Corby platform) will lose half a minute north of Bedford. But the 377s have much better acceleration than any current EMT stock, and they will make back that half minute - and more - on acceleration alone. Dwell times (currently 90seconds) may also be reduced to 60 seconds.
Taken together, I would expect a 100mph limited EMU to be around 1-2min quicker to Kettering (calling Luton, Bedford, Wellingboro') than existing rolling stock. 110mph offers little additional benefit and is not needed.