alright, let's get a few things straight here:
There is a huge difference between J-10 and the so called "twin-engined" J-10.
There is no question that the most we can hope for J-10 is to achieve A2A capability of Rafale/Typhoon. Maybe at home with supporting ground based radar and AWACS, it will also take down a few F-35s.
However, this "twin-engined" J-10 supposedly will already have many of the 5th generation attributes like sustained supercruise without using afterburners, using internal weapon bay, advanced RAM, stealthy engine intake, generally achieve some level of stealthiness (although probably still an order of magnitude greater than F-35/F-22), multi-role AESA radar, advanced EW suite and such. In terms of maneuverability, I would think the requirement would be higher than F-35/eurocanards and probably matching that of F-22. In fact, they will sacrifice multi-role capability to achieve more power tracking range in A2A, greater maneuverability and stealthiness.
Now, whether or not this will happen is a different story, but that's the goal. Remember, in 10 years times, the computer processing speed, RAM technology, missile technology and such will all have advanced.
As for stealthy targets for SAMs, you can check out Ba-7. That's what China uses as it's stealthy target to test against. It supposedly simulates the maneuverability of a 4th generation fighter. And it has very low infrared signature and radar signature (< 0.1 m^2 frontal and even smaller with RAM).