Don't do it!

Yes, the antifreeze solution is slightly more viscous, and has slightly less capacity for absorbing/carrying heat energy from the engine to the radiator.

But these are small disadvantages (easily overcome) of antifreeze solution when compared to the substantial disadvantages of pure water, two of which are:

1) Boiling point.
You cited that the boiling point of pure water is raised only 7 deg on 50% antifreeze (compared to 0%), but my antifreeze bottle's chart shows both 13 deg raise (i.e., 225 deg boiling point) at atmospheric pressure as well as 63 deg raise (i.e., 275 deg b.p.) at 20 psi radiator pressure. Granted, that's more than the Volvo spec's cap, but you can interpolate some substantial raise in b.p. temperature nevertheless.
There are also substantial benefits at running the coolant at higher temperatures (i.e., using a higher temperature thermostat), including higher thermal efficiency (i.e., fuel mileage), which a pure water coolant wouldn't be able to tolerate.

2) Corrosion protection
I can't imagine what condition your coolant passages in the engine block would become if you only used water. True, the water wouldn't electrolyze your block because it couldn't remain pure water for long (dirt, etc.), but it would certainly rust out. Try leaving a metal bolt in water for long and see what it turns to.

There is also a third, slight advantage, as water pump bearing lubrication from antifreeze additive.

And if you want to slightly increase your heat transfer, you can add a small bottle of some additives which are actually like a soap, to prevent bubbles (of air, which insulate) from forming and blocking heat transfer from the metal water jacket's walls to the coolant -- that will negate some of your objections to a antifreeze solution.