I have a question for some of the knowledgeable people on this forum. If the max allowable weight is 5 kg, and you are able to make this weight with whatever combination of equipment you select, what's the best trade-off, reducing the all up weight even further, or selecting the best equipment you can while keeping the weight under the 5 kg limit?

I'm thinking that the opportunities for systems optimization lie in the following areas:

Servos - You can choose lighter servos, but maybe at the cost of power, speed, resolution, holding power, etc.

RX Batteries - You can choose smaller capacity Li-poly RX batteries, but at the cost of having less capacity, having to use a regulator with the posibility that it might fail, and being unable to charge as fast as other battery options let you charge.

Props - You can choose smaller, and / or lighter props, but maybe at the cost of reduced efficiency, which can result in increased power consumption, or reduced thrust, or both.

Wheels - You could use foam wheels instead of a more durable pair, which might result in them wearing out, or tearing, when flying from paved runways.

Main Batteries - You can choose one of the lighter series of Li-poly batteries, but maybe at the cost of having a lower C rating, which means that the battery has higher internal resistance, which means that it will heat up more during a flight, which might require you to add additional ducting inside your plane to direct more cooling air over the battery, which could result in additional weight and complexity. Also, a battery with a lower C rating won't last as long as a battery with a higher C rating, which means that it will need replacing more often, which offsets the lower original cost of the battery.

Some of the areas where I don't think compromise is required are as follows:

Being frugal with glue
Using a carbon fiber spinner
Replacing the wing tube with one from PGB
Making sure that all servo leads and battery leads are at minimum length
Replacing the landing gear with a carbon fibre f3a landing gear set from Bolly
Using aluminum wheel axles
Using a spread spectrum radio so you don't need an antenna tube.
replacing the screws that came with the plane with shorter versions. (I saved a gram!! ...)

My current thinking is that as long as I can keep the weight below 5 kg, I prefer to use the following:

Sullivan lightflight wheels so I don't have to worry about them wearing or tearing.
An A123 1100 mah 2s1p RX pack without a regulator because it's simple, long lived, robust to abuse, I can fly up to ten flights without recharging, and it'll charge in ten minutes or less.
An APC 21X14 prop, because the power in the air is excellent, and it seems to draw considerably less mah from my battery pack, which lets me use a smaller, higher C rated battery.