A meta-analysis of sleep studies suggest both "too little" sleep is associated with stroke risk, while "too much" sleep is associated with heart disease and stroke risks:
Francesco P. Cappuccio, Daniel Cooper, Lanfranco D'Elia, Pasquale Strazzullo and Michelle A. Miller, Sleep duration predicts cardiovascular outcomes: a systematic review and meta-analysis of prospective studies Eur Heart J (2011) 32 (12): 1484-1492.doi: 10.1093/eurheartj/ehr007
In their conclusion, they state:
Currently, there is no evidence that sleeping habitually between 6 and 8 h per day in an adult is associated with harm and long-term health consequences. However, sleeping 9 h or more per night may represent a useful diagnostic tool for detecting subclinical or undiagnosed co-morbidity. People reporting consistently sleeping 5 h or less per night should be regarded as a higher risk group for cardiovascular morbidity and mortality.
In the results they explain a little more of the robustness of these results:
In the pooled analysis, short duration of sleep was associated with a greater risk of developing or dying of stroke (RR 1.15, 1.00–1.31, P = 0.047) with no evidence of publication bias (P = 0.30) and no heterogeneity between studies (I2= 0%, Q = 4.34, P = 0.50) (Figure 2A).
In the pooled analysis, short duration of sleep was weakly and not significantly associated with a greater risk of developing or dying of total CVD (RR 1.03, 0.93–1.15, P = 0.52) with no evidence of publication bias (P = 0.46) and no heterogeneity between studies (I2= 0%, Q = 3.42, P = 0.97) (Figure 3A).
This is evidence of correlation, not causation. Some confounding factor might affect both sleep and stroke risk.
I have not attempted to demonstrate personal productivity effects or over all mortality risk. I have just to shown that the short sleepers don't get by completely "without penalty"