Just my take on the problem......

Does the new hotend have a thermal break in it or does the teflon tube actually contact the nozzle?
If the latter is the case, printing at 250 will more than likely cause problems with rapid deterioration of the teflon tube.

If your infil is 100% you are basically printing a solid block of ABS, if the splits are on the layer lines it would suggest that the cause is the thermal difference in the mass of the print at various stages.

Can you use say 20% infill?