It's not quite clear from your question whether you plan to remove both the existing between-joist insulation and the fiberboard and put the new boards between the joists or if you are planning to install them over the joists for a faster insulation.
- I suspect you are planning to remove it all and put new insulation between the joists.
- Note at this point that it may be more cost-effective and especially labor-effective to use spray foam while getting a superior result (directly attached to subfloor without any gap, perfect seal to the joists).
Now to your question of foil-sided or not. I really see only very limited benefits of the foil in your climate in a crawlspace location, considering you are using 3-4" polyiso boards so you are getting an R-value of 21-28. At that point, the temperature difference between the inside face of the insulation and your house should be minimal.
Contact me directly if you want to discuss this further, and look seriously into home foam insulation instead.
For more information:
Read Dietmar Lorenz's Q&A "I need to add insulation beneath my wooden floor. What materials or systems do you recommend?"