I bought a planetx carbon stealth tri bike so I could do the Balla half. At the time they were £1500 and came with Ultegra groupset. This bike was easily the best specced bike for the price.
Although I had tri bars fitted to my road bike the position was not as agressive as the Stealth. Lots of hours on the bike in that postion will be needed unless you have a flexable back.
My road times certainly came down once I had the Stealth, (not sure about 45mins worth though), and this had to be because of the bike, there was just no way I had improved that much. I’m guessing it was down to how light and stiff(all the power going through to the rear wheel) the bike was, but problably the biggest factor was the aerodynamics with my body position on the bike.
Just my two penneth worth, the Stealth is an awesome bike.
Good luck with the Ironman.
Hope this helps.
Cheers Si