Isn't the Lexus IS250 supposed to be a 3 series equivelent?
except it is much slower, and the driving feel is so terrible on it that it feels like you just have novacane shot into your arms and feet.
the IS250 is terrible .
it is a 3 series equivalent for people who are buying say a 328i with no options on it just to drive to work. in that case its better than a 328i.
if you actually like driving, well first yo'd get the sport pack on the 328i. and then you'd not ever touch a is250.
as for the OPs question. I had a first gen G35 coupe and i'd say the infiniti's are about as close as you'd get, but its still not bmw feel. it handles great (in fact in instrumented tests it might actually handle better), but the engine is rougher and different (it is really really hard to beat an inline-6 or inline-4 for smooth). the steering at least on the G35 I had was good, but it was just a touch less i suppose telepathic as a 3 series (at least a properly equipped sport pack 3 series).
the new G37 honestly might be a little worse as far as feel, as its been more luxuried up, and is maybe a little softer than the first one, yet has a worse engine note do to the even more over bored out engine. the 370z is more or less the same (the 370z honestly is much more liveable than the old 350z, but its lost some of its character i think, its almost like a G37 with 2 less seats)