Tikkas aren't necessarily "slow", they simply tend to have longer throats and less aggressive lead angles which don't build pressure as quickly. This also means they can typically take a little more powder to achieve "book" velocities. The 129 ABLR would be a better choice than the 142s, but I've found that entire line of bullets rather difficult to achieve either the velocity or accuracy delivered by other bullet lines of similar weight and form.
On the 20" CTR + 127 LRX:
We killed a several deer and antelope, a handful of coyotes and four or five elk with the 127 LRX out of the 20" CTR. I don't recall seeing a single one of those animals taking more than a couple steps after bullet impact, and I never had one fail to exit. I distinctly remember one cow elk at over 500, that little bullet went through a solid 4' of elk and exited… and the elk bounced it went down so fast. Initially I loaded them for the kids to hunt elk with, but they turned out to be excellent killers on everything so we just kept shooting them.
IIRC, we were running the 127 LRX right around 2800 with 45(ish) grains of 4350. They were not the most accurate bullet in that rifle, delivering groups in the 1" range.
If you're chasing the velocity dragon, then a 20" gun ain't the way to go… that's just physics. As Lance said, it'll speed up a little after 100ish rounds, but I think I only got about 50-75 fps once the barrel "broke in".
If you're looking for a good combination of BC, Velocity, and killing performance out of the 20" CTR, then the Berger 130 HVLD or OTM is probably your huckleberry.
The 130 Accubond was another reliable killer, was easy to work with, and shot in the 2850 range. Kids killed a couple antelope and one deer with them before I moved to the LRX.