Help choosing suitable stall ratio for converter

Upgrade from 727 to 42RH is nearly there. I have found out that the stall of the converter currently fitted to my 42RH is 2300.
The car is geared for 130MPH at 5000 RPM, so 26MPH per 1000, 2000RPM at 52MPH. If overdrive comes in at 55MPH and lockup around 65MPH, then driving on main roads at 60MPH in overdrive it will be ticking over at 5000/130 x 60 = 2300 x0.69 for overdrive = 1590RPM. Way below stall speed.
My main reason for changing to overdrive is for comfort and to save fuel but I want to retain as much performance as I can. Is a 2300 converter going to cost me serious miles to the gallon on main roads? Obviously it will be ok on the freeway when locked.
The car weighs about 3500 pounds, 185/15 tires (26.5in diameter) with rear axle ratio of 3.09:1
Thanks for any help