Hi Wild Child,

Every degree lower is worth having especially in the summer months when you will notice more "Heat soak". When stuck in traffic for more than a few mins and they you get the chance to boot it again, you will notice a drop off in power then. Granted on the run at motorway speed you will probably get enough cold air in to be very similar. I have looked at the design of the std system and infact it is pretty good and allows for "forced" cold air into seal air boxes. Whilst I think you set up looks pretty mint, I would strongly suggest 2 mods for you to gain better performance.
1) re fit the cold air feeds and direct them into the front of your cone filters so you get a "forced" cold air flow.
2) fit some heat shield in place to isolate your air filters as much as possible from the engine bay.
If you decide to give this a go, please post how it all goes and what gains you notice. My guess would be standing starts will be improved most.