I'm jealous of your IP ranges. I have a single IP. As you are evaluating pfSense and will wan't to take advantage of it's enhanced security, I would think seriously about redesigning your network.
Not knowing what you use the internal networks for, or if you deliver any services externally, it's hard to say what you should do.
NAT offers another layer of security, some flexibility, but a little more complexity, but the benefits outweigh the risk of changing things.
Your ISP is routing to those /25's for you to /30 IP on your WAN, Yes. So..
I would probably create a /24 NAT (maybe 10.x.x.x) on your LAN using Private IP's and a different /24 your DMZ (172.x.x.x) and/or Wireless access on your OPT1 interface.
Put any services you deliver externally in the DMZ and statically NAT any IP's to one of the public /25 IP's that you have. The other IP's I would probably use for internal user services like VPN, PPTP etc.
This would give you a great deal of flexibility for growth, and security.