When I first bought my car I got a 240mm flat, but it was too small so I upgraded to a 270mm flat.
The 270mm worked pretty well for a while. But after getting into one of my colleague's car and seeing the difference with his convex mirrors, I decided to get a set of convex myself and I must say it's a big difference.
I got a set of the 270mm Broadway Convex w/ Blue Tint @ a local SuperAutobacs, and it matches my LX interior perfectly.
Trust me, once you try the convex, you won't go back to a flat mirror... EVER.
Oh, and to answer your question, since your car has no tint the blue Broadways will work perfectly. Because even with my 35% tint, I can see perfectly fine even @ night.