You're loading for a .30-06 hunting rifle, right?
If that's the case, I'd just stick with your 58 grain load. You'll never notice the difference that a few tenths of an inch of accuracy will make in any hunting situation, even way out there.
If you really feel the need to experiment further, you can try increasing or decreasing by 2/10 of a grain each way until you reach 57.6 or 58.4. You could shoot groups of 3 with each of these loads. However, don't kid yourself: this activity will be little more than playing on your part because a hunting rifle with hunting loads (especially in a cartridge like a .30-06 that takes up to 60+ grains of powder) is unlikely to be that sensitive to slight variations in loading.
Let me tell you something: I've worked out an awesome load with a 168-grain TSX in my .30-06. I did it by .5 grain increments. In a hunting rifle, I couldn't care less for 63.7 grains or 62.2, for example. My load, set at exactly 64 grains of N560, gives me 1/2 m.o.a. and it absolutely hammered a large mule deer at 300 yards with one shot. I doubt that finessing this load further would make any real-world improvement. In fact, I know it wouldn't. I found that 63.5 gave essentially identical performance.
For hunting loads, keep it simple. Full length size your cases, or at least back your die off so it is partially sized. Choose a load that seems to work well, and stick with it. Try it a few times to see if it works consistently on different days. If it does, and it gives you anything approaching 1 inch for three shots at 100 yards, you are done. You should spend the rest of your time practicing.
The next thing I would do is find a cheaper 165-grain bullet and work up a load that shoots to a similar place on the target. (In my rifle, I've found that the 165-grain Nosler Ballistic Tip shoots to the same point of impact as the 168 TSX with the same charge of powder) I'd then leave the scope set where you want it for the TSX and load up a bunch of the cheaper loads for practice.
You should practice shooting in all positions, including sitting and prone. If your range has a steel gong, try to shoot it offhand. This is where you will really get familiar with your rifle and get ready to make a good shot in a hunting situation.
Remember: after you've got the load worked out for your rifle, the real work of shooting and practicing begins.
