I've also thought about the topic a bit and have ridden both TT and "converted" road bike frames.
Re using a "converted" road bike frame: I wouldn't do it. The front center (distance from BB to front axle) is shorter on a road bike than on a TT bike. If you keep the same position, you would put more weight on the front wheel. TT bikes are usually also built to steer slower and go better in a straight line, which you would sacrifice - your setup would be twitchier.
Re light setup: two frames that seem lightish are the Quintana Roo PR6 and the Parlee TTIR Disc (claimed 1200g frame weight). I am attracted by the TTIR Disc, because of the convenience of disc brakes vis-à-vis integrated rim brakes. For example, I currently ride a Trek Speed Concept and avoid changing wheels at all cost because the rear brake is a complete b**** to adjust. Disc would make that way more convenient. Plus the benefits of braking better, which can be interesting on hilly courses.
A thought for you: if you want to go light, don't stick to the 808 and Super 9 disc: for example, the Citec Ultra disc is a whooping 250g lighter (1075 Super 9 clincher vs 825g), their 8000 Ultra front wheel is another 160g lighter. Both very under rated products imho, but technologically interesting and good for real world use.
Have fun with your project and share what you settled on!
good points on the wheels mate. I suppose i've just been hesitant to change the disc + 808 because of the initial price outlay.
I considered the handling issue... i wonder if that could be negated by using a TT bike fork with a more relaxed steering angle.
I've had a look at that 2016 cannondale slice black.... could be a beauty in all black.
Once again cheers for the input.
I've got one more race (Ironman Wales next weekend) on my current Argon E112 and if I'm lucky enough to get a ticket to kona I'll get some kind of build thread on the go for the new race whip.