Two GTS 450s will also cost more, use more power, give off more heat and take up more room in your case which can complicate air flow and cable management. Check out the performance per dollar chart on the techpowerup review. The GTX 460 has the SLI setup beat slightly and can always be counted on to deliver that performance, not just in games that scale well and always right when the game is released. The GTX 460 also overclocks even better than the GTS 450 so that isn't a plus. As for noise the cards both come with a wide variety of coolers so the numbers in the guru3d review are basically meaningless unless you plan to stick with the reference coolers for some reason.
Two GTS 450s are a good deal and are in general faster than a GTX 460 but there are other considerations which favor a single card setup to the point where SLI is still better used as an upgrade path rather than being best choice to start with.