One of my sons is highly gifted and has dyslexia. We had him privately tested when he was in 2nd grade because the school kept dragging its feet-- I'd known for 2 years that something was going on and I kept being told reading would "click" in the next few months, which never happened, of course.
I think it's great that your son qualifies for an IEP. Mine never did, but he has an excellent 504. We also had to pay for a private tutor for 2 1/2 years. (He's 9 in 4th grade.)
5x week with an o-g based program sounds excellent to me. Wilson and O-G are pretty much the gold standard in dyslexia remediation and you're lucky the school will provide it. Just make sure the instructor is actually trained in the program. If not, that's a violation of IDEA. Make sure the school sets measurable goals for his progress, i.e., "he'll be through 2 chapters in 6 weeks, reading at DRA xxx."
You'll also need to keep track of whether your child's IEP is actually being followed. This has been a constant battle for us, as my son doesn't seem like he needs the accomodations on his 504, but he does. He's supposed to be doing all his writing work on the computer, but his teacher never makes it available, which, again, is a violation of IDEA.
I had to fight for his gifted services, too. They did "classify" him as gifted 2 years ago, but it was only this year that he finally gets the pull-outs (which I actually think are pretty worthless.) He also now qualifies for the district's HGT program, but we don't think it's the appropriate setting for him, so we aren't going to use that option until middle school.
But here's the good news, 3 years after diagnosis, he's 1.5 grade levels ahead in reading and writing! That's not up to the potential of his IQ, but we're thrilled with his progress and expect him to do even better in middle school. The "scaffolding" his 504 gives him has actually worked to help him build up his skills and improve.
My advice is to be very proactive, educate yourself as much as possible about what's available for your son, use an advocate if necessary (we brought an outside expert in dyslexia) and ensure that his IEP is being followed. Also, bring donuts to every school meeting.
