It's been the same on my 750, 2600k, 3770k, and 4771. I don't have access to a turbo CPU right now (sold for upgrade), but I found an old video I took of UT2004 running on the 2600k that demonstrates classic turbo behaviour (please excuse the quality):
http://youtu.be/KLebLUsLVG0
The 2600k's turbo steps are 3.8GHz for one core, 3.7 for two, 3.6 for three and 3.5 for all four. UT2004 is a single threaded program, and there are no other programs running. You don't even see 3.8 GHz at all. Well maybe I can give 'turbo' the benefit of the doubt and say that driver overhead is putting a (tiny) load on another core. It should then at least be running at a stable 3.7GHz. But no, it spends half it's time at 3.6GHz, constantly changing, and even dropping to the lowest 3.5GHz turbo state. What good is that? The game is single threaded. The temps and TDP are nowhere near max. Maybe if you set up a completely synthetic test like Prime95 on one thread turbo might 'work', but that's no good to anyone.
The concept makes sense, and if it worked properly in real-usage situations it would be great (especially for 6-8 core processors), but my experience with it makes me think 'turbo' is barely any less of a stupid gimmick than 'GPU boost' (a truly pointless feature if ever I saw one) .