The OP asked about a GK 700RBII, which is a solid-state amp rated to safely handle cabinet impedances as low as 4 ohms, so the amp would be at no risk here. The cabinet on the other hand has an impedance of 8 ohms and a power handling of 300W, then your GK 700RB-II could theoretically blow it, since it can produce 320W at 8 ohms. But as long as you don't turn the volume all the way up, you'll be fine.
Here's more info than you asked for, because I'm bored waiting for a build to finish at work:
Think of it as "more ohms == more resistance to current flow". So more ohms means less
current flow. Less current flow means less power is drawn from the amplifier.
Solid state (i.e., transistor-based) amps can only supply so much current/power before the transistors start to exceed their designed Safe Operating Area
and literally overheat. Your GK has been designed such that it can safely power a 4-ohm or higher
speaker combination without overheating. Some bass amplifiers can safely run at 2-ohm impedance, but 4-ohms is most common.
The other factor to consider is "effective impedance" when you hook up multiple cabinets to a single-channel amplifier (most bass amps are single-channel). The formula for parallel resistance can be found online, but by far the most common scenario is two 8-ohm cabinets, which yields a 4 ohm effective impedance. As you could probably guess, two 4-ohm cabinets would yield a 2-ohm effective impedance. Because your GK is only rated to safely drive a 4-ohm load without overheating, you would therefore not
want to hook up two 4-ohms speakers to it! But two 8-ohm speaker cabinets would be OK (in fact, this is how I run my GK 700RB-II).
Is your amplifier so powerful that it could blow out your speaker cabinet at max volume? Just compare the amp's power output to the cabinet's max power handling at the given impedance. If the amp is more powerful than the speaker can handle, then don't turn the volume all the way up!
Some people are also confused by power handling when two cabinets are in use. Let's say you have two 8-ohm cabinets, each rated for 200W. These will have a 4-ohm effective impedance when hooked up to the amp. Let's say the amp produces up to 500W of power at 4-ohms. The power gets "split" evenly between the two cabinets, such that each one only "sees" 250W maximum. So theoretically, you could
blow both speakers at max volume in this made-up example.
If you have two cabinets with different
impedances hooked up, the calculations get messier. It's not a good idea anyway.