So this pretty much confirms that Barcelona's single threaded performance is not up to par with Core 2's performance, even in SPEC_fp test. However, due to its native quad core architecture, Barcelona can catch up to Clovertown in rated tests, notably in SPEC_fp rate test.
So making their quad core "native" was, IMO, not an option, but a necessity. As you can see above, core-for-core performance speaking, Barcelona is significantly lagging behind Core 2. But with superior scaling, AMD can still remain competitive in this field. Now all they need to do is to bump up the frequency.
Thanks qurious, very nice find.