Installing the higher ratio rockers will increase the valve accelleration rates which in turn, will require a stiffer valve spring to prevent valve float.
However, the reason why the engine maintains a decent idle is due to the fact it will lower the duration at 0.200 lift because the area under the curve and ramp rate is reduced. Also remember that when you increase the valve spring pressure rates, you are also increasing the lifter plunger loading.
Some day I might have a set of OEM roller lifters sent to be modified to take the additional spring pressures. There is a company that does such modification:
Sherman Racing Products
P.O. Box 1326
3245 Hwy. 1 South
Donaldsonville, LA 70346
Cliff Sherman (225) 473-4923 or (225) 717-1460
J. Allen Sherman (225) 717-146