SPI speed will be listed under Electrical Specifications, in the form of required delays.
Keep in mind a scope generally won't continuously dump data to the computer. This could exceed viewable speed. Instead, you have a triggering event, capture say 256 samples, and you may not begin capturing on the next triggerable event if it's too soon. But capture speed is still very important because that affects your max sampleable frequency. 100ksamp/sec would not correctly read components above 50khz (Nyquist rate).
Note that the 30F series has pretty high power consumption at high speeds, and it's not as fast as the lower power 33F. There's faster 33F devices up to 1.1Msamp/sec IIRC, and the processor's up to 40MIPs. You probably need a USB port for sure though. There's also the new PIC32 line, half the product tree has USB.