The Intel HD 4000 is significantly more powerful than the old Radeon HD 4250 which is based off of the Radoen HD 3xxx series. The Intel HD 4000 is not a performance graphic core though. It is basically equal to a desktop Radeon HD 5550. The older Radeon HD 3000 in Sandy Bridge CPUs are basically equal to Radeon HD 5450.
The Radeon HD 4250 basically falls in between the Intel HD (I refer to it as the Intel HD "1000") and the GMA 4500.