Which bike to use for hilly race?

Wildflower HIM bike course is tough. i dunno if the olympic is the same.  however the graph you show has very little flat parts.  if you are more comfotable in the saddle on your roadie i would use that.  lots of climbs and descents.  might help to save your legs slightly for the run.

best of luck!

The only question for me is will you spin out of the road bikes lower gears on descents . Otherwise, the road bike has slightly lower gears for climbing and you are more comfortable climbing and descending on it . Have you considered a test ride on the coarse on each bike ? Just a thought .

I'm not familiar with the wildflower course, but are you basing your opinion on it being hilly from looking at the profile you posted, or because you've actually seen/ridden the course.  From the looks of the profile, it doesn't look that hilly IMO.  Elevation profile graphs can be very deceiving depending on the scale of the X and Y axis. 

In any case, I'd use the TT bike regardless.  It's why you bought it...use it.

If it were me.

Climbing, I am seeing about 6% grade at the worst ? You should be able to do that with a 39/28. I don't find my road bike climbs much better other than gearing and I think your gearing is OK either way. So I see little advantage for the road bike on the climbs for that course. Besides, the 34/25 will not be a lot easier.

On the descents, you need to figure out if/how much faster you will be on the road bikeor tri bike. I am much more comfortable at high speeds on the road bike, but that's because I am a big chicken. I would say I'm easily 3km/h faster. There seems to be more downhill than flat. If you are really kamikazee, that 53/11 could have you flying. But will you be able to take advantage of it, or will you be braking at 60 km/h. Are you comfortable at very high speeds  on the a tri bike ? I am not.

On the flats, I may be 1 or 2 km/hr faster on the tri bike. But if I am 1 or 2km slower downhill, it's break even. There is only about 4-5 miles of flat.

I would say, it depends on how much faster you think you can go on the downhill with the road bike or the tri bike, but it's probably close to break even for me. But again, I am a big chicken on downhills and prefer the road bike at very high speed.

I agree with everything you said and your logic except for this part.  I actually see about 13 miles of flat on that graph.  Unless you consider  ~1% grade hilly/ 

On your uphills .... you probably won't be able to tell difference between 39X28 and 34X25 ... do the math ... almost same ratio. So first you should ride the course. We have a hilly course in Maryland for Columbia Tri ... and I thought my roadie would be better but nope ... tri bike is a lot faster for me. No question. But I regularly, routinely hit 50MPH on some of our downhills around here. Just this last weekend, for instance, on Teen Barnes Road. So Columbia faster for me on a tri bike, but, maybe not Wildflower, for you. In that case roadie is a good call. But re: swapping cassette ... 11-28 does not always work with old Ultegra ... especially with compact crank. (11-28 works most of the time, but Shimano recommends NOT using 11-28 unless you have the newer 105/5700 or Ultegra/6700 or DA/7900 group). Instead of swapping cassette, I'd think about sliding the seat forward on the roadie, so that the saddle tip- to-handlebar center length is same as your tri bike ... and then installing a cheap set of aluminum clip-ons from Performance or similar. (OK, I understand there's a lot more to a tri fit than the saddle tip-to-handlebar length ... but this would be a good compromise for one race where OP wants hands on brakes for the big downhills).

Actually, I changed my mind. Ride the tri bike. Ride within your ability on the downhills. You'll be fine. It's a race ... that's what you got the tri bike for.

The tri bike is the faster choice.  The road bike may feel better climbing but will not be substantively faster. This isn't magic. Your body can put out so many watts, and your body weighs a certain amount. That is how fast you will climb. Unless the TT bike is made of iron, or your aero bars don't allow for any reasonable out-of-aero position, you should climb 'the same'

Descending, if its REALLY a problem you need to tweak the bike or fit. Some aerobars with upturns at the brake levers might help if you don't have those.

And it is important to remember that even up to an 8% grade for an average amateur rider, an aero frame that is a couple hundred grams heavier is still faster than a round tube frame that is a couple hundred grams lighter.

wind still exists uphill!

The fast AGers and pros will be on tri bikes, disc wheels, and deep fronts. You should be too unless you are worried about safety on the descents.

You are right, I forgot the flats at the top of the hills.