I have a 6.5TCU I used in Wyoming last fall for antelope. 120gr Nosler Ballistic Tip, 2,050fps, shot a 'lope at 255 yards in the shoulder, exited about 1 1/2" hole. Dead shortly after. My barrel was a 14" that Gary Reeder but a long muzzlebrake on, so effective length is about 12"
Your 6.5TCU will be fine for deer.
I have a Burris 2X7 with the Ballistic Plex which worked great.