Personally, I'd rather go for the 550cc and over-do the spec slightly rather than running the 440cc that bit closer to their safe operating limit... but thats a personal thing, also, depending how much further you go power-wise you could retain the 550cc where you would almost certainly need to upgrade from the 440cc in the future.
I'm running a VF34 on my car Joe, it spools pretty quickly and is always on the money when making progress... I seriously rate my car the way it is and I am really wary of upping the power too much more because it could potentially spoil what a great back road car it is.
Haha, yea I think the 95RON map could feel a wee bit flat after rolling around on the high boost map!!
Cheers,
Grant