This hasn't been done much, and isn't likely to be done. Pseudotheraphosa apophysis and some Lasiodora species are also in the running for largest and or heaviest. Measuring spiders already in captivity doesn't mean anything, since many of the large tarantula species seem to get a lot larger in captivity. Common food for most tarantulas depending on species and location includes many different insects, scorpions, other spiders, rodents, snakes, reptiles and amphibians. If they ever ate birds, the birds were probably dead or sick or tied up.
Birds do eat tarantulas, it's unlikely it's the other way around.
Beef heart is a popular food item for many large captive tarantulas. Many tarantulas will eat most anything if you cut it up in small enough pieces, including humans and blue whales. Tarantulas, some wolf spiders and many others tear the prey into tiny pieces and masicate it inot a bolus. The prey remains consist of non-digestible exoskeleton pieces, since spiders are liquid feeders. The nutrients ingested are very small in particle size.