Pfflowd setup with multi-wan

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My pfSense is setup as follows:  WAN is a T1 for servers and failover, OPT1 is High-speed cable for users, and LAN (soon to be about 10 VLANs).

I've got ntop setup on a remote box with pfflowd exporting to ntop.  The statistics are good, but it's been requested that I begin preparing monthly report of traffic on both internet connections.  Is there a way that I can set up pfflowd - in combination with a remote ntop - to report on the individual interfaces?  Local ntop can do it, but my firewall box isn't powerful enough to handle both - traffic slowed to a crawl when I enabled local ntop.

I would like to continue using pfflowd/ntop if possible, but I'm willing to hear suggestions.  If I were to switch to SNMP monitoring, could I do this?