Consensus amongst every piece of training material I’ve seen would be that this would have Negative impact. If you are properly training/building/tapering into your A race, don’t throw it off with a random race addition a week out.
If you just care about having a good time and enjoying two events, go for it. Definitely feasible to do both and likely at a high level.
If your A-race is a sprint, you are unlikely to have much in the way of a lengthy taper. That prior weekend is going to be your most important training weekend. I personally wouldn’t think a 2-ish hour hard effort would be the best training you could do to prepare for a sprint, where you are going to be going much harder and faster than what you would do in that Oly.
If you said two weeks before the A-race sprint tri, I would say it would probably be pretty good training for that weekend. But with it being only one week out, if I were coaching you, I would rather have you do more race-specific work on that prior weekend, and that certainly wouldn’t be an Oly effort. If you raced that Oly for real, you would build enough fatigue into your body that you would be feeling a bit messed up even out to mid-week when I would rather see you doing shorter pickup work instead of recovering from a hard effort.
That said, every athlete is different, and I am not your coach, so I don’t know anything about how well you recover from hard efforts, or how your body responds to various training loads and efforts.
The physiological half life of a workout is 7-10d. A fast workout today will benefit your fitness in 7-10d. It’s the recovery from the workout/race you should be concerned about, not the fast workout.
What’s one of the best way to insure you go fast for your A race? Reduce your fatigue levels.
I thought I read in this thread that the weekend before is the most important weekend for training. That’s probably the least important weekend for an A race. It’s the 12-16 weekends that came before that that are the most important weekend(s). And then the 12-16 that came before that and then the 12-16 that came before that and the 12-16 that came before that and the 12-16 that came before that etc
Or as I tell my athletes no workout is more or less important than any other workout. It’s the cumulative effect of working out for 6-60+ months in a row that really makes you fit