Do you think I would need a cooling upgrade if I were to move to an 84W Haswell part? I know people talk about worse IHS performance on them. I'm comfortable with higher CPU temperatures (80C? I assume Haswell has TJmax >100C?) as long as the peripherals are not getting overheated.
Providing you won't overclock that new CPU, you should observe an about 10°C increase, maybe something more (depending of the specific case), so IMVHO nothing to be worry about (about TJmax, given that an higher temperature shorten CPU lifespan, as a rule of thumb you should likely want to stay around 70°C at most).