Dave In my opinion and many others you already have one of the best drop'em in there tracks deer rifles. The .243. The federeal in 85 gr hollow points is said to be the ultimate deer cartridge. Rated better than belted magnums for dropping them in there tracks. Knockdown power is a myth there's no such thing. Velocity and bullet selection will do the damage, shock value is what kills instantly and the .243 does this well. I have shot and owned both calibers and I only shoot the .243 these days. I dont know why but my .270's never had the accuracy my .243's did.
Heres a link on the .243
http://www.udarrell.com/ultimate_deer_cartridge.htm
And heres another one.
http://www.udarrell.com/ultimate_dee...dge_guests.htm