The IS300 competitor is the BMW 3-series in general. The 323/325 and the 328/330 are both competitors b/c they are all in the same segment. The 3 series' performance could be better or worse than the IS, depending on the model you choose. Of course, the price for the 3 series will range from 30k to 45k whereas the IS300 will stay btw 31k and 35k. Basically, all IS300s will have similar performance, but not all 3-series will.
Toyota does offer manual, but Lexus has never offered a manual. Lexus has always focused on luxury so I can see why they were a little slow to see the importance of a manual in a performance sports sedan.