It should be decent. the i5-4200u is clocked at 1.6GHz standard speed, but Turbo Boost can increase the clockspeed to 2.6GHz if only one core is used or 2.3GHz if both cores are used (most cases). 2.3GHz is pretty respectable for a ULV (ultra low voltage) CPU. The great thing about it is it helps prolong battery life.
I recently fixed up a 15.6" Dell Latitude 3540 laptop which uses the i5-4200u CPU. It is comparable to the i5-2410m (2.3GHz / 2.9GHz Turbo Boost) in my 14" Lenovo IdeaPad Y470 when Turbo Boost is activated. Looking at a watt meter (Kill-A-Watt) the Dell 3540 uses about 12w - 13w when idling compared to about 23w for the Lenovo Y470; both screens set to 60% brightness. Probably could have lowered the Dell to 50% brightness...