You can either upgrade or submit a new application for platinum. However, holding both MBB2 Gold and Plat still earn you max Rm50 rebate only. Cr limit is depends on ur income and commitment but if the Plat application is successful, normally they will increase ur CL, in my case it was 50% increased, but after increase its still the lowest CL among all my CC , even though I use MBB2 the most.