I don't envisage taking up target shooting properly but I would like to play at it - I can safely shoot to over 300m on one permission. Not fussed by the weight really. I am assuming you have said this on another thread, but what have you concluded beyond the T3X with a 1:8? Is the Tikka stock not up to it as is?
'Problems' with the T3x Tikka stock come down to the fact that it is a 'budget' rifle and they have to save money somewhere.
1- 'Bottom metal' of the non-CTR versions is plastic, this is fine with the standard plastic stock but if you are changing the stock to a stiffer composite one then I would highly recommend it be changed. The CTR bottom metal is just fine, I have one and use MDT plastic mags with it (arguably better than the CTR mags, lighter, cheaper, single feed). Some reports of extreme setups with very heavy barrels which retained the plastic mag but changed stock (to accommodate the barrel) have noted that the whole action assembly wobbled, so the plastic 'bottom metal' was binned in favour of an AICS system (in-letting for one is another added cost, some chasis systems will accept AICS mags and eliminate the need for a 'bottom metal' entirely).
2. Relating to the above point, T3x models that use the standard and CTR mag systems are all the same length, so you can put a CTR bottom metal onto a standard T3x no bother (apparently there is a difference between the old T3's, the CTR version's mag well was cut differently). However, the standard mag system uses magazines that are all the same length, whatever the chambering. A magazine designed to take a 'long action' cartridge (.270, 30-06) is adapted to take a 'short action' length cartridge (.308, .223) with an internal plastic spacer. Some have modified the 'short action' mags to take advantage of the actual dimensions of the magazine and receiver, but you will still have the disadvantages from point 1. The standard mags themselves are actually a good design, very light and reliable. I have kept them them for my 'long action' setup but opted for a 7075 aluminum bottom metal that accepts them (from UK Gunworks).
3- Stock, one size fits none is the term that comes to mind. Very seldom will you find a factory stock with 'cast-off' (or cast-on), Monte Carlo style combs or adjustable length of pull. I think you can adjust the length of pull on a new T3x stock, and some of the CTR/Varmint models come with an adjustable cheek riser. I think the recoil lug in the T3x is now steel (old ones were aluminium), but they are still slid into the plastic stock and not permanently retained through bedding compound. Another point is that shooting off a bipod does require a reasonably stiff fore-end which is wide enough to distribute/dissipate the forces encountered before and after the shot, as well as attach the bipod in a secure manner (sling stud attachments are not a good solution, properly integrated picatinny rails are a good compromise) A good aftermarket stock eliminates these disadvantages and adds features to improve handling, reduce recoil and provide a better fit.
The standard stocks on Tikka's are very far from being bad, they are miles ahead of what you will see on the average 'budget' American-made rifle, its just down to picky people like myself who don't mind paying extra to eliminate the economised parts. Sometimes you will notice the difference, most often not. If improperly installed, performance may even be worse than the original components.
Tikka T3x strong points,
1- Great action, especially in stainless.
2- Nice adjustable trigger from the factory
3- Factory barrels usually good, but some enthusiasts replace them before the first shot is fired, a real waste!