You're in luck. The RX and by defalt HH are designed as powerful cars. In regards to emmissions, it mostly has to do with the exhaust system and fuel economy. If you drive a hybrid aggressively, the emmissions and fuel economy are going to be very similar to their non-hybrid counterparts.
Where these hybrids differ however is in power. 2006 Hybrid 0-60mph 7.3, 268hp vs. 2006 RX330 0-60mph 7.7, 223hp. Frankly I think its more fair of a comparison to compare the hybrid to the GX470 0-60mph 8.1, 263hp. Now compare those emmissions!
Off the light, My HiHy accelerates faster than my 2003 ML500 and 2006 R350. And yes, I get better fuel economy with less emmissions. With the new line-up from Lexus, the power user is bound to see the light. These are very powerful cars and the enviroment will benefit.