I've been considering two bulbs for my Sav (Bosc) as well, she is getting big and needs the coverage a bit more!
I would say worth a try for the cham. You plan to keep the basking spot the same, just raise the ambient temps near the top of his whole cage? Depends on the size of your cage too.
Personally I have a much lower basking spot temp than 45C but I have been thinking of raising ambient temps, I have noticed a very slight decline in activity levels/ increase in basking time of my male cham.