are we still talking about UR here or Mono Red? Against mono red you're pretty screwed. Against UR, you can positively crush their manabase.

As you said, they'll hold the combo as long as possible if you have a Trygon out. But if you're squishing their manabase, then there's no way they'll get the 6 mana necessary to combo in one turn. Hell even if Trygon is the only thing you have, they'll still have a harder time getting to 6 mana out because they run artifact lands, mox opals, etc that just get munched on. If you have some kind of mana denial with Trygon then all you have to worry about is welder (tutor for crypt). Trygon also puts them on the clock.