The 560 ti is a superior GPu to the 560. The difference is that the 560 ti has 384 stream processors to the 560's 336. Hence the price difference. An OC'd 560 ti may rival a GTX 570 or even a GTX 580, but only if those cards are not OC'd.
Essentially the MSI 560ti-448 is a downgraded GTX 570. It is much like what Nvidia did with the GTX 470 and its downgraded little brother the GTX 465. Also, you cannot mix and match the GTX 560 ti-448 with other GTX 560's in sli. The GTX 560 series uses the GF 114 core, while the GTX 560 ti-448 (and 570) use the GF110 core.
If you want to wait for its availability the ti-448 should be a better card than the 560 or 560 ti.