I doubt there's much difference in average speed between the LRC coaches and HEP coahces. The maximum speed of HEP coaches is 95 mph (not 90), and there are only a handful of places along the line with a speed limit above 95 mph anyway. The two train types are both subject to the same "P+" speed limit, so there's no difference on curves.
The Venture sets will produce a more significant travel time saving compared to HEP/LRC coaches because they qualify for the "LRC" speed category (which was named after the LRC coaches back when they had a tilting mechanism). While there are only a few segments with a 100 mph "P+", speed there are large portions of the Kingston Subdivison with 100 mph "LRC" speed.
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Many curves have an LRC speed limit (for Venture/Renaissance coaches) 10 mph higher than the P+ speed limit (for LRC/HEP coaches), which will allow Venture coaches to maintain speed much more than LRC/HEP coaches.
Curves through Belleville: Venture coaches can go 153 km/h, HEP/LRC coaches can only go 137 km/h.
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Further to
@Urban Sky 's comment, Via scheduled as little as 3h48 in 2014, and I don't think the track speeds now are any less than they were then:
One thing which has changed though is the dispatching from Toronto to Pickering, which is now done by Metrolinx rather than CN. From what I've seen, Metrolinx is significantly worse to Via than CN was. The increased GO train frequency and 2-track bottleneck due to Ontario Line construction don't help either.