The last time I took GO Bus Route 16 (Hamilton QEW Express) in the afternoon peak, it took a really odd routing - from the terminal down Yonge to Queen's Quay, to York, to the Gardiner WB on-ramp, Gardiner to QEW but off at Sherway Gardens, re-entering QEW from West Mall, off at Dixie Road ramp (North Service Road) and returning to the QEW at Hurontario. Then north on Erin Mills Pkwy to the 403 then the 407.
It was December 7, but weather wasn't a concern. The trip took 1h38, and that was just to Main/Longwood (I was heading to Dundas that evening).
The back-up westbound at Highway 427 can be bad too as the 427 also dumps a lot of cars on QEW, and you've got the merging and the lane that goes into Dixie Road off-ramp. Even weekends.
I think HOV lanes starting at Erin Mills would be a great idea, but I can't see any room east of there. I'd also like to see California-style HOV ramps to/from the 403 at Oakville and build the HOV lanes on the 403 through Dundas Street to connect to those.