The Kilo TT Pro and WT are quite a nice upgrade from the standard TT. I have the WT so that I can throw on studded tires in the winter and ride it around, saving the salty crud from getting on my road bike. I'd recommend the Pro or WT over the standard TT due to the better cranks (Sugino Track) and wheels (Alex SUB 30mm V-Aero section wheelset).
The first thing I see a lot of people mention changing on the standard TT is the wheelset. They ship with really crappy wheels, as mentioned by this guy:
http://www.bikeforums.net/showthread...91#post3008691
That same guy mentions how the Kilo TT is a good deal when it shipped with the Sugino cranks. Well, the standard doesn't ship with those anymore, but the Pro and WT do.
As for Pro vs WT, that's pretty personal. The Pro has a 1" headset, the WT has a 1 1/8". The former is more popular these days, the latter is more traditional. The former is more compact, the latter allows for fat tires when you want them. That's really the only notable difference, so you have to decide whether you want the sleek compact 1" headset on the Pro or the more versatile 1 1/8" headset on the WT. That, and the 2009 Pro costs about $40 more, but I wouldn't count that as much of a deciding factor. You shouldn't let two Jacksons come between you and the bike that suits you better, whether it's saving the cash or spending that tiny bit more.
As for the IRO Mark V, it is a wonderful bike. It has more aggressive frame geometry, so it's meant for riding fast, on track or off. That can make it a bit less comfortable, but you often sacrifice a bit (or a lot, but only a bit in this case) of comfort for speed. It's definitely worth the extra money. It was my first choice over the Kilo TT WT, but I passed it by wanting to be able to mount racks and snag groceries. A lot of people prefer frames without bosses for racks and fenders, but I wanted a more versatile frame. If you want to go to the track, though, definitely go with the IRO Mark V, it is hands down the better bike. Not to mention the care and service you get from Tony at IRO. You just can't beat that, the extra money doesn't feel extra anymore. It feels necessary and understandable if it is the right bike for you.