Forgot to mention the Oknas are both quoted with deluxe glass

You are correct that the Okna 500 series does not reinforcement, however I would not let that deter you unless you have excessively wide units. That model hits a design pressure of R50 with no reinforcement which is a rare feat for a vinyl window, and is a testament to its engineering and build quality. If you take pricing out of it and look at product alone, I'd narrow it down to a final 3 of the Okna lines and the Imperial LS. The Okna 800 is probably the nicest looking in most folks eyes, has slimmer lines (more glass area), and the best performance ratings of all of them. Is it worth $100 per window over the LS? That can be tricky to answer. Will you be well served by either choice? Yes. Does that price difference become less of a factor when you consider your choice over a potential service life of 30 +yrs? I'd say yes again.
I have two pieces of advice for you: 1) get the best product that you can comfortably afford. You will be happier with that purchase in the end. 2) It sounds like you are considering 3 or more different dealers in this equation. This aspect is HUGE. Even though they all check out on the review sites etc, I'd encourage you to really dig deeper on this. You want a company that you can develop a relationship with, that you feel confident will deliver excellent service AFTER the sale, that you'll want to do business with again, and that you will refer with confidence to your friends and family members. Remember that those prices don't just reflect the product, but the total package in installation and company that come with them. With that being the case, any one of those five choices could truly present the best value, only you can decide.