The only difference between the 2 is:
- Gold plated display and audio ports
(Gold is a better conductor than other metals so a little better audio)
- High-end nichicon audio capacitors
(Higher quality capacitors)
- Gaming 5 comes with 4 Sata Cables while Gaming 3 only comes with 1 Sata Cable
(More SATA cables)
Heres a comparison on the actual Gigabyte Website:
http://www.gigabyte.com/products/comparison/list.aspx?ck=2&pids=4959,4966,4953
Conclusion: Not worth it.
Also just a side note: You're not guaranteed to be able to hit 4.5GHz while keeping the CPU cool and stable, but the Gaming 3 shouldn't limit you, if you do. If you want more information on that, just ask. Also if you have any other questions just ask, too.