First off, apologies if this is the wrong forum. There are a lot of moving parts here, and I felt this question could go into any number of forums. Mods, please move if you think it fits somewhere else. Normally with enough research I am able to arrive a decisive choice, but in this case there is no clear or obvious winner, and I am in need of expert advise.

I have a BA flight from LHR-PDX flight in June. The departure time is 3:40pm, and I am in J. I booked the flight many months ago with Atmos points, as I was unsure of my France itinerary but wanted to be confirmed in J at a minimum to return to the States. A surprise to me, I am finding no feasible flight options from CDG-LHR that would enable me to self connect. BA has only three flights that day (it's a Saturday), with either a 60 minute (too short) or 7h (too long) connection. AF is slightly better, but still not ideal. One flight has 1h55m connection, and with transiting from T4 to T5, I think it's too short. The other is a 5h connection, which is plenty comfortable, but looking at how early I'd have to get to CDG I started to think Eurostar from Gare Du Nord might be just as good of, or even a better choice.

I have never taken Eurostar, but my understanding is one should arrive at the station around 90 minutes prior to the scheduled departure time. My ultimate question: would a scheduled arrival to St. Pancras at 11:30am afford me enough time to make the journey to Heathrow T5 for a 3:40pm TATL flight on BA in J? Or, is it recommended to take the one-hour earlier departure that arrives at St. Pancras at 10:30am. I understand there are a few options to get from St. Pancras to Heathrow T5, taking anywhere from 50m to 1h10m.

I'm curious if anyone here has negotiated any of the above options, or if anyone sees fault in any of the above logic. Lastly, I checked ORY but all it had was one unusable Vueling flight.

TIA