Disclosed are certain novel polyester compositions particularly useful for shaping or forming into containers and similar shaped articles by thermoforming procedures. The polyester compositions comprise a thermoplastic polyester, an impact modifier and a polyester crystallization rate enhancing component selected from poly(tetramethylene terephthalate) homo- and co-polymers. The polyester compositions exhibit improved crystallization rates as compared to similar compositions not including impact modifier or compositions using other types of crystallization rate enhancing components such as polyolefin-based polymers.