I would say that a RIAS of 123 and a K-BIT of 134 is a rather significant spread... and since the RIAS does have a tendency to underestimate, I'd say that result is suspect.
I'd say that the question of whether you should pursue further testing depends on your goals. You already have two tests that identify your child as requiring gifted education services, and the school has agreed to provide them. So if that was the goal, I'd say mission accomplished.
Both tests are of the quick-screening variety, so if there's a reason you might need more data, then I'd push on to the WISC. Reasons might include the school not doing enough for him and using his RIAS score as justification, suspected learning disability, desire to qualify him for DYS, etc.
