Been there, got the T-Shirt when I wanted higher upload speeds aswell when adsl max was the only option at my phone exchange. BT Retail didn't do it, and BT Business also didnt offer max premium as it competed with there SDSL Product which wasn't available in my area anyway.
In the end I opted to go for an Entanet reseller using their office 15 product which was good for me as I'm at work all day when the 15gb limit was in force, and after 8pm and weekends it was unlimited useage.