Figuring out what affects my speed

This morning I'm flying my sim Baron 58 towards KVYS, and I notice
that my airspeed is about 217 kts, much higher than usual. I'm level
at 5000 feet MSL, altimeter is 3038, clear weather, throttles full,
mixture set for peak EGT roughly, props set to 2520 RPM, about 150 RPM
below redline. The temperature outside is -1° C.

The mystery for me is that 217 kts (slightly in the yellow arc) is
unusually fast. I'm not sure what I'm doing different. Usually I'm
just below the yellow arc in cruise at this range of altitudes.

So throttle, mixture, prop, and altitude can surely affect IAS in
level flight, but what else? How much does the gradual burning of
fuel make a difference? Would it boost my speed by 20 kts or more as
it burns off? I started out with almost a full load of fuel, and now
about half of it is gone.

I'm just trying to figure out what factors I may be overlooking.

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