Had a customer that had poor latency and higher bandwidth through the AC earlier in the day. Customer failed over the H/A pair earlier and reported overall network improvement, even physical machines going to O365 showed improvement. The ADC is just gateway, DDC XML, WEM and SF vips (nothing else should be routed/proxied through it) . I wanted to see if we can back track on any VIPS that might have shown higher throughput over the past few days, Looking at historical (a few days back), how can I review the historical newnslog files for which virtual servers and their throughput?

Newnslog is not going to give performance numbers. You would need to be monitoring them with NetScaler Console