Rate-Distortion Optimized Quantization (RDOQ) is an encoding optimization technique that may be modified with no implications to the bitstream compliance with the standard. In the paper, we propose an RDOQ variant with exact cost estimation resulting in higher compression ratios as compared to HEVC Test Model. This improvement is obtained at the cost of the complexity increase that may be scaled by replacing the individual steps of exact estimation by the simplified ones from HEVC Test Model. In that way, a family of RDOQ variants is created. The performance of the exact variant from this paper defines a kind of the performance limit for RDOQ.