Power PLUS attitude = Performance
On my A330-300, set 2.5 nose up and 78% N1 for S + L flight at most weights.
You should also know what sound levels to expect in the cockpit from the Airspeed in cruise.
If you think that you might indeed be too slow then set CLB detent and lower the nose to 0, wait till the noise level returns to near normal then set it back to 2.5 and 78%.
All the while checking the GPS groudspeed from the FM to use as a gross error check whilst flying the Aircraft as smoothly as possible until I exit the area and hopefully all returns to normal.
Anytime I approach an area of suspect wx I cannot avoid I try to do 4 things:
1/ sit the cabin crew down, 2/ check the current GS and listen to the noise
levels, 3/ note the current attitude and N1 to achieve current speed and finally 4/ brief the FO on all of the above just incase all hell breaks loose.
I've done this for the last 10 years or so. Why did I consciously do this? Because our Airline has had it's share of Iced up Pitot static systems causing overspeed and stall warnings On the 744, 777 and A330 types where the crew did what I suggest above ( ie: fly the damn plane on Attitude and N1 ) to a successful outcome.