hi Briscoe
I cant remember if the Le Meridien Hotel is in the vicinity of Heathrow or not but if it is I would just get a taxi to T4, I have stayed at the Rennaisance Hotel a fair few times and have travelled to T4 by car and it has been a 5 minute drive, what you dont want to do though is sell yourself short, dont you just hate it when people are late for their flight and the excuses you hear are nothing short of astounding, like "but the carpark was full, I couldnt park" .
If you opt for the T1 route and get the Heathrow express then I would leave yourself ˝hr as I think the buses frequent every 15 minutes or so?
Hope this helps
Dean.
p.s. someone may have a better suggestion