The X-Bolt has a three locking lug design. The bolt throw is very short on the X-bolt but some people complain about how the bolt works. As you open the bolt, it will click and then stop but the bolt is not fully open yet. You need to push it a bit further and you will hear a second click and now the bolt can open. The bolt can be opened while the safety is on. The X-Bolt is all metal design except for the magazine and of course the stock itself. Browning stocks are left hand and right hand specific. The X-Bolt comes in many stock designs however I believe lefties are limited to Stalkers and Hunters. The X-Bolt comes from the factory with a pretty decent recoil pad. The rubber coating on their synthetic stocks are well known to peal. The X-Bolts scope mounting system is purely proprietary although just about every manufacture makes the bases for the gun.
The T3 has a plastic bolt shroud, plastic trigger guard, and plastic magazine. None of these should be an issue. The bolt is a two locking lug design. The stocks are neutral cast while only the T3 Forrest is left of right had specific but good luck finding a T3 Forrest. The T3 and T3x can not open the bolt while the safety is on. The T3 has a recoil pad that is as hard as a hockey puck. While this makes for a very durable pad that is resistant to ripping and pealing, felt recoil is more. The T3x recoil pad is a little bit better but still not as soft as a Limbsaver recoil pad or even the Browning X-Bolt pad. Changes with the T3x is a metal bolt shroud, some changes to synthetic stock to make it modular. You can change the angle of the grip, make the forgrip wider, and add a raised cheek piece on most models with synthetic stocks. The stippling on the stock is different and has a much more course grip than the T3. The ejection port on the T3x is a little bit larger in order to allow easier single round drop in feeds. The T3 and T3x can use their proprietary Sako Optilok rings and bases but is also dripped and tapped for Leupold STD and DD bases as well as Weaver bases.
With the gun being a 30-06, the recoil pad being hard may not be an issue unless you go with a Tikka T3 Super Lite.