In my case, at 40 degree C bed temperature, strength is increasing with increasing elongation but at 50 degree C, slight decrement is observed in strength and %elongation.
It depends of the material. For exemple for PLA an optimal temperature is between 20 and 60°c and for ABS around 100°c: http://www.verbatim.com.au/technotes/3D_FAQs.pdf
According to Deng et al. a sufficient platform temperature is essential to avoid severe deformation even it is a less important parameter for PLA than ABS : http://www.sciencedirect.com/science/article/pii/S0360132316301731