LHR is pretty bad using any airline for connections.

IF you do use Ryanair they make it pretty clear that they aren't accountable for any missed connections due to delay or other reasons.

Thanks to FT, I booked a return flight in The Biz on bmi to LAS from MAN (leaving at around 10am). I'd arranged to meet MrLapLap in the US and he was travelling from Tokyo (it was cheaper for both of us to get to LAS than for me to get an economy filght to NRT). There were only 3 bmi flights to LAS from MAN per week so I wasn't prepared to miss it. Even though there was a connecting flight to MAN from LHR early that morning I refused it and travelled to MAN the night before instead (slept in the airport).

You might want to talk to a travel insurance company and find out from them what they consider to be a reasonable connection (i.e. which route they'd be prepared to cover) and go with that.

Personally I'd rather take my chances with an early flight from Stansted (even if it is FR who I've used a lot and have rarely suffered delays with) over one from LHR - no matter how reputable the airline was.

Go to Dublin the night before. You might even have fun there.