The 250s do start to thump at about 100gr or more.
105gr of BH209 and the 250gr should be close to 2000fps. Not bad IMO but i would like to see the results on game. It should be fine with the high SD.
The modded plug does look really cool. Ive got a older Knight NFPJ plug i would like to try modded like that in the 45cals. The big 50cal pocket on the Lehigh plug can grab a patch occasionally if you run it down into the BP vent pocket. Im more curious though about performance differences (if any) in the 45cal.