I have an IRO and it's a great bike for the value. I have a 59 frame (6'3, 190) and it's great for my needs. Casual rides, under 10 mile commute. The bike is stiff enough for my needs, although I can't really compare since I've only had two bikes. 69 GI and 700x28 tires make it comfortable enough for commuting.

Just to throw this out there, you'll probably want a frame that supports fenders since I see you're in DC. I have the Mark V Pro and had to get the clip on fenders, which is OK, but not the best option during the winter. Also, in calculating your budget, you'll need to consider the cost of a helmet, lights, locks, etc.