What is a fast built in op-amp to use in OrCAD Pspice Capture? Or how can I design one?
Pick an appropriate op-amp, download the Spice model from the manufacturer and install it in Orcad. 

This TI document Using Texas Instruments Spice Models in PSpice
covers it, with the specific example of the THS4131 145MHz fully differential op-amp. 

Follow all the instructions-- you need to add the library as indicated or you'll just get errors.