Yes flashes can be over heated if they don't have thermal protection. Below some recycle times based on battery chemistry and number of batteries.
SB-800
Number of batteries
Min recycle time
Alkaline-manganese
x4
6.0 sec.
x5
5.0 sec.
Lithium
x4
7.5 sec.
x5
7.5 sec.
Nickel
x4
6.0 sec.
x5
5.0 sec.
NiCd
(1000 mAh)(rechargeable) x4
4.0 sec.
x5
3.5 sec.
Ni-MH(2000 mA)(rechargeable)
x4
4.0 sec.
x5
2.9 sec.
Fresh Batteries
As you maybe aware firing the flash at less than full power also increases recycle time. Can you just move closer. What type of recycle time are you looking for.