I'd go for the wheelchair too. Although I haven't had to go to T5 yet, I requested one last summer for T3 whilst I was down to 1 crutch and hobbling following an accident. I phoned the airline and booked it the day before, had a little wait at the check in desk for the wheelchair to come, but the guy was lovely, let me stop at travelex and the lounge to freshen up, whilst en route to the plane (short of time, despite being there 4hrs early, t3 is vile, but CX was great!)
Anyway, meant being whisked through security etc, preboarding, and lots of TLC from the crew. At HKG was met at the gate with a wheel chair, who took me to the lounge, and promptly came back for me later for my flight to AKL

Worked wonderfully well, despite the guy who collected me back at LHR constantly telling me how mean people were for not tipping him and how sore his feet were!

Wouldn't hesitate to use them again if my ankle was bad, no point in putting yourself in agony before you start your journey