Glad to, do not mind explaining my rational about my opinions. First to admit they are what they are, opinions and there is more then one way to skin a cat if you will.
First off the criteria was for a part time deer rifle for hunting out to 350 yards and to also be used as a target rifle out to 750 yards.
Well be both agree that the 6.5 mm family of bullets certainly covers these two types of shooting nearly perfectly.
With the release of the 6.5-284 factory brass, I guess this round is a bit easier to load for then the 6.5-06 AI but not much.
All that is needed is to take a factory 25-06 case, seat any boattailed bullet of at least 100 gr over a near top level powder charge and touch it off.
No need to even neck up the brass as the 6.5 is only 0.007" larger then the 25-06 and you will not even be able to tell a difference seating the Boattailed bullet in the case. Must use Boat tails though!!
Other areas that lead me to the 6.5-06 AI are my preferred action, the Rem 700, to build on.
True the 6.5-284 can be chambered in the short action version of the 700 but if you seat the long VLD bullets out where they should be, you will be shooting the rifle in single shot mode.
Certainly not a huge disadvantage but as a big game rifle somewhat of a pain.
TO get a repeater with the 700 using the 6.5-284 with long seated bullets you will need the long action, here is where the 6.5-06 AI has some advantages over the shorter round.
First off, the Rem 700 long action will handle all rounds up to 3.700" long in most cases. This allows those long 140, 142, 155 gr class VLD bullets to be seated just to the base of the neck and still have plenty of room in the Rem 700 LA box.
With bullets seated in this position, the 6.5-06 AI will produce 100-200 fps more velocity then the 6.5-284 with all other vaiables being equal. The velocity range will depend on barrel quality and barrel length.
Again as for a target or match rifle, this is meaningless in every way but in a big game rifle, the added performance will provide slightly better on game bullet performance, not much but some.
Now lets get into feeding, the 6.5mm-284 can be a little ****y as far as feeding goes because of the rebated rim and short fat body with relatively sharp shoulder angle.
The 6.5-06 AI is much longer and skinnier then the 284 and while it has a slightly sharper shoulder, it is a much smoother and reliable feeder, especially when the rifle is worked rapidly such as in a hunting situation.
So I guess my opinion is that if we were dealing with a strictly target/match rifle, I would go with a SA M700 converted to single shot and use a long seated 6.5-284.
For big game hunting, I see the higher performance and feeding advantages of the 6.5-06 AI being a benefit to the deer hunter.
I am first to admit that I am splitting hairs here but there are a few to be split. I just like the 6.5-06 AI as a big game rifle over its shorter competitor.
Of course, I have been playing with my 6.5 WSM in my XP-100 handgun that I just got finished. I will be using this handgun for my big game hunting this season.
I have been pretty rushed without alot of time to develope a lot of loads but with the 120 gr Ballistic Tip, I am getting 3100 fps out of the 15" Lilja barrel and with near 50 three shot groups down range so far, the largest to date is .881" ctc and it has printed 28 groups in the 3's with the smallest being a .197" three shot group ctc.
This little number could be the next great 1000 yard round. Will have to see how the throat stands up but in a rifle, 3200 fps with a 142 gr Sierra MK should be quite comfortable out of at least a 26" barrel.
Good Shooting, hope I answered your question alright without rambling to much.