I have noticed how much lower my terminal velocity is since losing over 4 stone in weight. I chased @nickyboy down off Holme Moss a few weeks back and couldn't keep up with him because I am now 2 stone lighter than him. If I had still been 2 stone heavier than him, he would have been chasing me instead!
Chase him uphill and turn the tables on him.
In the past I cycled with someone who was quite big. I couldnt live with him on the downhills, but on the uphills he was so far back he was nowhere to be seen.