This question has been the basis of two major, landmark trials in the peritoneal dialysis community, the CANUSA study (named as such because it looked at PD patients in Canada and the U.S.A.) and the ADEMEX study (looking at PD patients in Mexico).
The CANUSA study was a prospective cohort analysis; the original analysis suggested that higher total solute clearance–which is calculated by adding the PD solute clearance to residual renal solute clearance–is associated with an improved mortality, and based on this analysis a recommendation of maintaining a higher total KT/V (>2.0) was recommended.
However, the results of the ADEMEX trial–the largest prospective, randomized controlled trial to-date in PD patients–showed paradoxically that increased PD solute clearance conferred no survival benefit, and rather that residual renal function was the primary predictor of survival. A subsequent re-analysis of the CANUSA data–which had made the now-recognized-as-incorrect-assumption that the residual renal function KT/V and peritoneal dialysis KT/V are simply additive–showed a similar result as the ADEMEX trial, namely that residual renal function is primarily responsible for any mortality benefit seen in the group of patients with a higher KT/V.
Based on these results, the current KDOQI guidelines recommend a lower target KT/V of 1.7.