Both rifles are "classics". The Marlin 1894, especially if it has the nice walnut stock, is probably the higher quality rifle, but the .30-06 is by far the better and more versatile hunting rifle. You mention:
what i am concerned about is would I be losing or gaining in range/hitting power.
If I had a .30-06 (or .308 Win) for hunting, I would think of the .44 Magnum Marlin as a self-defense carbine (short rifle). Self-defense against humans, that is, or maybe charging boar. The big fat 0.44" diameter bullet, particularly in 250 grain (heavy!), even more in hollow point, is a slow "bumble bee" round that will deposit a ton of energy in soft flesh at short ranges (25-75 yards). Tremendous stopping power. In pistol self-defense "school", we are taught that the ideal penetration depth is about 12" into the animal (human). Ideally the bullet stays in the target, to avoid overpenetration and damage to objects (and people) behind the target. The .44 Mag from a carbine gives you this kind of "terminal ballistics" at the distances I mentioned (from handguns, shorter distances).
The .30-06 bullet, by contrast, is only 0.30" diameter, travels at nearly 3000 feet per second and spins at 150,000 to 180,000 rpm. For most .30-06 loads, at a range of 25 yards, the bullet just drills a small-ish hole through flesh and keeps going at lethal speed for another 1000 yards or more. Extremely deadly but not the massive knock-down
* power (= flesh destruction) of the fatter .44" bullet. The .30-06 has much longer range, hundreds of yards (would you use a scope on either rifle?), and the low flesh damage is exactly what you want for relatively delicate, non-dangerous game like deer - it's a shame to mess up the backstraps with blood/contusion if you're a little off the frontal chest/lower neck aiming point.
All in all, the rounds these two rifles shoot are very, very different. Not to say you couldn't hunt with the .44 Mag (more sporting) or defend yourself with the .30-06 (the M1 Garand infantry rifle was .30-06 for a long time). They are just very, very different. There's more to learn. Do you feel like studying ballistics? You can find the info on the web.
'Nother pointer: Use a title for your thread that asks a specific question or says "teach me about X". Your title "Need advice" does not attract many readers and answerers.
* As discussed many times on THR, the wording "first-shot stopping power" is more realistic than "knock-down power". The "knock down power" of any downrange round can, at most, be equal to the recoil you felt when shooting the firearm, which you withstood easily without falling down. If you want to learn more, search on these terms or ask further in this thread.
