if you dont bore the intake, you will cause turbulence in the air flow...you will feel like the car jerks when you release your throttle.
when the air comes passes through the throttle and hits the wall,it cause the flow to be disturbed and this can even cause loss of power....you definitly need to get the intake bored to have the throttle work as it should...
another thing...having a larger throttle + intake..improves air volume , but reduces air velocity, if your head is not ported, the performance difference in using a larger throttle might not be that significant...because air volume has increased,but the air is not being pushed out quickly enough due to restriction in the flow...(sifus,please correct me if im wrong)
is your cams also stock?
get a Type R intake....with a type R intake and larger TB you'll make more power at high rpm,but you'll lose out abit on lower rpm ranges...with a ported head...then the power gains should be significant.