Sorry for late reply ...
That makes a lot of sense considering the specs of the Mikrotik stuff. Many of my own hours have been taken up trying to push a square peg into a round hole !
Primary reason for asking was the cost of the hardware platform, a 5 port gigabit Routerboard 750G or GL runs to around £50 in UK. The current hardware platform I'm running pfsense on Jetway Atom MB with 5 gigabit ports is more like £175.
My experimentation with the Mikrotik RouterOS on PC platform, I found it difficult to use, since I'm more of a windows hacker than command line. Pfsense on the other hand is very well laid out and easy to do what I wanted, multi-wan attached to single private lan.
Anyway, I'm happy with what I have it works well, and was a lot cheaper than the alternative Draytek Multi-Wan solution that I was looking at.