Despite the PR about the speed increase, in my opinion this project was intended primarily to reinforce the electric power supply in the North Jersey segment of the NEC. The work included added capacity at the Metuchen frequency converter, a new substation at Hamilton and various other improvements designed to solve chronic catenary voltage issues along that section of the NEC. The catenary work was an adjunct to that.
The problem with increasing train speed is the need for shorter catenary span lengths. The span length issue is not due to structure strength but the need to limit catenary movement created by the pantographs at speed. The longer the span, the greater the catenary movement (by a square factor). The existing PRR spans are in the 225-250 foot range. Those spans, originally designed for 80 mph operation, are right at the limit for 135 mph (if not longer than ideal). Spans in the 150-175 foot range are needed for higher speeds. In order to get shorter spans where there are now longer spans, new structures are needed and a lot of them. A 23-mile section of railroad would need about 700 new catenary structures. At about $200,000 each, that is $140 million just for structures. Given the logistical complexity of installing new structures on the NEC with very limited work windows due to traffic and power constraints, that estimate could be low.
I have no inside knowledge, but my guess is that the desire for higher speed lost out to the fiscal reality of the expenditure needed to achieve higher speeds. There will be a segment with constant tension and shorter spans, but some of the original catenary replacement work is now limited to hardware replacement on the existing structures while retaining the fixed termination design.
The completion of the power supply enhancements will fulfill the primary goal of the project.