[strike]You won't be able to get as much out of your CPU with an H81 motherboard. A Z97 is capable of increasing voltage and will therefore allow a higher overclock given sufficient cooling.[/strike]
[strike]I have one of those MSI H81M-P33 motherboards and it doesn't allow you to increase the voltage, but I know it allows to increase the multiplier;[/strike] so you should start out by going up +.1GHz from stock and see if it runs stable. Then move up +.1GHz each time checking to see if it's stable.
*Edit: Actually I found out that that board with a G3258 DOES allow for voltage increase. But with 4690K or 4790K voltage increase is not available on the MSI H81M-P33. Some chips just aren't as lucky as others and overclocking isn't a guarantee.