Interbeat Interval (IBI) from photoplethysmographic recordings (PPG) is usually employed as a surrogate measure of R-to-R (RR) time series measured using the electrocardiogram. A lot of research has been devoted to proposing accurate fiducial points in the PPG to provide IBI with good agreement with the RR time series. Nevertheless, less attention has been paid to the relationship of this agreement with the PPG quality. This work uses a simple signal quality assessment (SQA) index based on the autocorrelation function (ACF) of the PPG. It compares its values with the agreement between IBI and RR time series using, simultaneously, two different measuring instruments (Biopac PPG sensor sampled at 1 kHz (BS) and Empatica wristband measured PPG sampled at around 64 Hz (ES)) in 31 subjects each one monitored around 25 minutes. We provide tools to synchronize both systems and correct sampling frequency disparities before agreement assessment to make fair comparisons between measuring systems. The ACF SQA index is defined to vary from 0 (worst quality, random noise signal) to 1 (best quality, periodic pulse generator). Wilcoxon signed-rank test shows that median ACF SQA is significantly higher for BS than for the ES (median ± interquartile range: 0.81 ± 0.09 (BS) versus 0.78 ± 0.07 (ES); p<1.4·10-6). The same test shows that agreement between IBI and RR, measured as the median of the absolute value of the differences, for ACF SQA larger than 0.85 (good quality, (GQ)) is significantly different than for ACF SQA lower than 0.85 (fair quality (FQ)) for both systems (BS: 2.74 ms ± 1.18 ms (GQ) vs 3.68 ms ± 2.06 ms (FQ); p<8.2·10-5 and ES: 7.94 ms ± 8.03 ms (GQ) vs 14.1 ms ± 11.7 ms (FQ); p<2.6·10-6). Identifying PPG signal segments with high ACF SQA opportunistically provides IBI time series with a better agreement.