I found my own solution. This code will filter out mailbox sizes over just under 1 GB.
SELECT TOP (1000000) tblExchangeMailbox.DisplayName, tblExchangeMailbox.Alias, tblExchangeMailbox.RecipientTypeDetails, addresses.email AS EmailAddress, tblExchangeServer.AssetId AS ServerAssetId,
tblExchangeServer.Name AS ExchangeServer, tblExchangeMailboxStatistics.TotalItemSize
FROM tblExchangeMailbox LEFT OUTER JOIN
(SELECT MIN(Address) AS email, MailboxId
FROM tblExchangeMailboxAddress
GROUP BY MailboxId) AS addresses ON addresses.MailboxId = tblExchangeMailbox.MailboxId INNER JOIN
tblExchangeServer ON tblExchangeServer.ServerId = tblExchangeMailbox.ServerId INNER JOIN
tblExchangeMailboxStatistics ON tblExchangeMailbox.MailboxId = tblExchangeMailboxStatistics.MailboxId
WHERE (tblExchangeMailboxStatistics.TotalBytes > 900000000)
ORDER BY tblExchangeMailboxStatistics.TotalBytes DESC