Whisper maximum range

[WhisperFan]

We have all heard that even a little .22 can go three miles when shot .... but what about the 300 Whisper.

A ballistic calculator indicated that a 220 gr SMK fired at 1050 fps will do the following:
If you are sighted in at 200 yards:
You will be 16.5" high at 100.
You will be 21.4" low at 250.
At 300, you've lost 51.8"

FWIW .... at 500 yards you are 267.6" low (that's 22.3 feet low)

So - my questions are:

1) does anyone have first hand experience at firing the 300 Whisper at ranges beyond 250 yards? If so - what were your impressions?

2) What is commonly considered the maximum effective range of this caliber in subsonic loads?

I am know the the 300 Whisper has been used for years in handgun metallic silhouette. But it looks like it would have some trouble in rifle silhouette.