What is your current scan time? What are you trying to keep it under? What precisely is the scan time concern? Maybe an HSIO could help solve?
You can sometimes optimize your logic to reduce scan time. Also, there's certain logic operations like copying large number of bits or numerics, or string manipulation that you can optimize. Usually the "slow" code is isolated - maybe it does not need to be executed every PLC scan, for example (do some work this scan, other work that scan).
If scan time is critical, a 2nd PLC can maintain the original PLC's scan time. Does the remote I/O control need to be dependent upon the logic in the current PLC, or does the remote I/O control only need its input states (no Cs, no Ds, no Timers).
If it truly is a different control cell altogether and you truly only need the X input states, you could get a 2nd PLC and then write the X input states from the original PLC using a WX instruction to the remote PLC. But if the logic between the two is dependent on each other, other than just the X states, you will need to stick with a single PLC with a remote base (BX-DMIO or H2-EBC100 or T1H-EBC100, whatever is your current I/O platform).
If you do go with a 2nd PLC, the latency on the X input state of the original PLC will be slightly slower in the remote PLC (a scan or 2 behind), and even miss some "edges" if the X input states are changing very fast relative to PLC scan time (HSIO may be helpful for processing very fast discrete inputs BTW).