The proposed study examines the simultaneous influence of factors (environment, type of task, and product properties) upon functional user states that critically affect assessor performance during the realization of various online tasks. In addition, test environment format varies as individual vs. group one, to assess whether testing conditions affect the test results. The test uses two types of tasks that, respectively, induce user functional states of anxiety and monotony/fatigue. Differences in product features are represented by two university website layouts with high and low aesthetic quality, as measured by website aesthetic quality index (U-index, our earlier elaboration). We have employed two groups of metrics to measure user performance, directed at both cognitive and emotional components of the user states. For cognitive efficiency, intellectual lability and productivity of cognitive operations were assessed. Emotional stress was measured by four metrics of self-assessment, namely the level of anxiety, fatigue, excitement, and confidence. Two assessor groups were put in conditions of individual vs. group task solving. Within each group, sub-groups were assigned either anxiety-inducing or fatigue-inducing tasks. For each task, subgroups worked with webpages of either high (U-index > 17) or low (U-index < 8) aesthetic quality. As the test results show, group task solving enhances the synchronous impact of website aesthetics and task features upon the user states. Interaction of high-quality design, group environment, and a monotonous task provides for an antagonistic effect: aesthetic layout in a group environment significantly reduces the fatigue rate. Low aesthetic quality in a group environment leads to cumulative effects in combination with any type of task: for monotonous tasks, it contributes to the development of fatigue, while for anxiety-inducing tasks it grows anxiety, and, in both cases, productivity drops.