I have had 3 jackets over the years "an off the peg" leather one that cost $300 in 1980 a MCnatty leather one that wore outafter many years use and finally a Stenvaag Canvas/leather one that cost me $1100 via TSNZ about 4 years ago (Skorpion is the latest variation). This was by far the best one and worth the investment. I normally advise my shooters to go for a tailormade one if they can aford it as the jacket fits your body shape better. As Fluff says shoulders are important. The jacket must pass the overlap test esp if shooting outdoor.

The difference between the $300 Shooting Stuff type off the peg and the $600-800 ones are quality of manufacture. Iwould expect the $600+ ones to last a lot longer, fit better

One of the Wgtn guys has a Gehmann mid-range canvas one that cost him around $600 this looks good value, passes EC
Others are using the "club" type ones

Suggest look at what the top shooters are wearing. Most have an old faithful that still passes EC others upgrade at various times. It all comes down to personal preference. You spend $4000+ on rifle but balk at $600 for a jacket

It just I'm not sure on spending $600 on a jacket that might only fit for 6 months and i've asked a some M Grader i know about buying shooting jackets and they told me what to look for in a bad jacket.
The thing on my rifles is i inherited both of them from my dad who spend a little bit to much on rifles so I didn't have buy them.

I guess you answer your own question here Zack, if you are still growing then its not worth spending good money on a jacket that will only do for a little while, and I would suggest that you A, find a good second hand jacket that has still got a few 10.1s left in it, B carry on using a club jacket (so long as the club will let you), until you feel confident that you are not going to grow too much more.
The McNatty jackets had a few more adjustments than most others and are quite axceptable for club shooting and if neccessary you can mor permanantly secure those adjusments for championships etc and release & resucure them as required to cater for your growth. I think Darryan Miller still makes them.