LCY it is; 20 minutes check-in, and I've rarely had to wait more than 5 minutes for security. You can't say that about either function at Heathrow, and at T5 if you don't get to the security point by 35 minutes before departure they don't let you through. The gate is about 7-8 minutes from the train platform (actually it's directly through that concrete wall alongside the train, but you have to go through the terminal. See here

http://maps.google.com/?ll=51.504008...06856&t=h&z=17