Ive looked at the Q50, but the reviews are not all that great. The steering sounds awful....after all its not just about power, also I've previously owned a 350Z, and the engine into Q50 is essentially still the same as the Z's but with an electric motor stuck on, so it'll be abit like a backwards step for me ;)
But more seriously though the IS300H is for my wife, and for her mpg > bhp any day of the week, and actually I enjoyed driving the IS300H much more than I thought....hence my very brief/fleeting thought about getting something similar for my self.
I don't do many miles in the 335i so mpg is not really an issue, and have spent about £7K on modifications to the engine/suspension/ICE over the last few years, which means even though from the outside it looks like a 320D, it's capable of delivering 90% of the performance/fun of a M3, but without the 'M' tax. Recently did a 2000 mile+ round trip around Europe in the 335i, including 8 Alpine passes, 140mph+ blasts down the Autobahn with the wife asleep in the passenger seat, and the Belgium GP....So it will take some thing very very special indeed to tempt me away from my 335i, the Lexus dealer tried it, but I put a stop to that conversation within about 10 seconds
The only car on the market that I can realistically seem my self letting the 335i go for is the Tesla S....but at nearly £100K for the model/spec I want, I think I'll be holding on to my 335i for a long long time yet, which really is no hardship .