"Did you read the footnote?"
Oops. My prior response was on my phone, so I wasn't actually able to read that footnote. Incorrectly recall it being an "up to" bandwidth note, not a note about on-board gig interfaces.
The reason, though, for the on-board gig interface footnote, module slots, for additional interfaces, often have bandwidth limitations that don't support the full bandwidth of the ports the module might provide.
As your 4331 should have 3 on-board gig interfaces, in theory, depending on the hardware architecture, over 2 Gbps could be passed between them. (Technically, for wire rate, you need a PPS to forward 3 Gbps, and a "fabric" to forward 6 Gbps. BTW, for wire rate for you gig link, you'll need forwarding PPS for 2 Gbps and "fabric" for 4 Gbps.") Whether the CPU can support that, is a different issue.
In my prior reference, I mentioned the Miercom benchmarks. Page 12 of the report, shows the performance analysis of the 4331. What you want to note, is how the impact of the same bandwidth, using different configs, impacts CPU usage. For the "complex" services features, the 4331 struggles at 300 Mbps. I.e. the boost license probably won't help.
However, for simple service usage, there's a lot of untapped CPU available, enough, perhaps, for about 2 Gbps.
So, again, whether a boost license will allow you to take full advantage of a gig link, is unknown with only the information you've provided.
What you might do, is note current CPU usage for various traffic loads, and assume (because isn't always true) you can linearly "scale".
