Just came across this thread...
I love the iCourier and have five of them! The fastest is a simple canyon racer (652 / 885 m/s), so no good for what you are after and although it is shielded and has a couple of weapons, I don't think I'd try to fight in it.
Then I have this one, which was my original combat build. Not particularly fast, but certainly effective (and sometimes I'll swap out the PA for a missile rack, which increases speed a bit).
A ship builder, outfitting and comparison tool for Elite Dangerous
s.orbis.zone
I also have a couple of others that are more multi-role, planetary vehicle hangers and the like, and they are a similar speed. But I always wanted a fast combat build, and finally this is what I came up with.
A ship builder, outfitting and comparison tool for Elite Dangerous
s.orbis.zone
Not quite the shields that you are after, but I haven't lost them yet as it's fast enough to get out of harms way.
As has been mentioned, the downside to the iCourier against larger ships is the weapon size. I typically use these against NPC pirate lords in Corvettes, and it's just a bit tedious without the help of system authority and takes ages picking away their shields. It can be done, particularly the first one with the PA, but I usually reserve these ships for missions that take me to high or medium security systems where I'll end up with a bit of help from system authority.