Coyote is right
Since the idea is versimilitude, the only reasonable approach would be to run it as you would have run it before. Any modifications would be cheese. These Orcs don't know any better.
I guess you could introduce a dash of caution since the PCs will be in obviously better armor, and the weapons might look better. However, the issue becomes at what point do the Orcs get a clue and wave off the attack?
I mean if I'm Mr. Mook Orc, and I see a party with fighters wearing very nice plate armor, with little rocks floating around their heads, and wizards either engaging in overland flight, riding phantom steeds, or otherwise manifesting significant power, I will not screw with the group. Orcs may not be real smart, but they probably aren't that dumb.
I guess the question really is, how outwardly apparent are the manifestations of the PCs power. Are they still dressed like a level 4 party? If so the orcs should act the same. If they appear to be rather higher on the food chain, you'll have to be careful at what point the Orcs would simply pass. The simple truth is that either the Orcs are plenty dumb and willing to attack anything, which means any preparation is probably out of character, or if smart enough to prepare, they are likely to back off.
buzzard