Northern Light
Superstar
A reduced capacity of about 10%, it's not massive. The OL has more capacity than the existing subway as well - it's not some low capacity line.
Some of the savings are from the technology change, yes, but most of it actually come from surfacing the line along the Lakeshore Corridor and elevating it further north and at Exhibition. The alignment went from around ~7km of tunnels to ~4.5km of tunnels to get from Queen and University to the Danforth, a ~35% reduction. The entire OL line only has about 8.5km of tunnels on it's 15km corridor length, and that's where it really saves on costs.
The technology change is a big reason the line makes so much sense anyway as it is what enables a lot of things like shallower stations, surfacing along the Lakeshore corridor, etc., and still provides roughly 2x the capacity of projected demand on the line.
Make no mistake, the OL is not some brainchild of Ford himself.. I somehow doubt he's a transit aficionado looking to make innovative changes to subway system designs. I suspect the OL was pitched to Ford by Metrolinx, which had previously published similar ideas (i.e. a subway connection from downtown to Exhibition to take pressure off of Union Station for the GO system). Ford simply backed that decision, which I think was the right one in the end.
He's also making stupid mistakes elsewhere, like burying Eglinton West.. But I think people are right to give him credit for genuinely pushing these projects forward as quickly as possible. There is a clear eagerness for his government to get major infrastructure projects actually underway ASAP, unlike the Liberals.
The segment from just east of East Harbour, to the next tunnel segment at about Pape is 1.7km - Mx suggests the price difference for burying vs tunnel for this segment is 800M .
I don't know if we have a net number for the remaining differential segment (Parliament to East Harbour), undoubtedly there are some savings though there are material off-set costs as bridges will have to be built/enlarged and some full-sized Hydro Pylons moved/buried as well.