Wait...so youre telling him to scrap speed work for rep stuff? And then instead of traditional speed work, do olympic lifts? What do you want him to do and why do you want him to do it...or are you just regurgitating some shit you read elsewhere?
There is no magic number at which getting faster will suddenly become effective. How about a 148'er who benches 280 raw? Will speed work be ineffective for him? How about a female who benches 250 raw? Will it not work for her?
Maybe what you meant to say is that if you dont have any MUSCLE..dynamic work will not be as effective...and I would agree with that, but making a blanket statement like "if you cant squat 400 lbs, then speed work wont do anything for you" is kind of dumb. Especially when you go on to tell him to essentially do another type of dynamic training.
OP, what I do is use my speed days as an opportunity to 1) focus on technique and 2)go heavier on my assistance work. For example, I do speed bench, and then work on going through a rep/set/weight progression on floor press in the 5 rep range.
That way I can set a pr of some sort on floor presses and it gives me something to get amped about on speed days.