5.5m/s or even 6 m/s is like jumping off your house; with a good PLF you can survive it , but probably not without injury. I think the Bhpa advice is underlining that the faster descent rates are "survivable" but probably not without injury and considered "acceptable" only because it's an emergency last chance when you need to deploy.
I'd much prefer to jump off a wardrobe than a house and have done what Steve is doing and changed up on both my reserves (at some considerable expense but ,I consider worth it, if only for the extra peace of mind. I've gone for Gin one-G 42).
A good Plf is still recommended and shoild be practiced (who does? I don't), but the descent rate is much preferable: You pays your money (alot) and takes your choice.
Fly safe .