yes, all transferred, outstanding & TPs from Gold -> Platinum. Took them around 7 days to do this.
yes, new cards <-- new GST to be imposed. Better upgrade before your Gold imposed with GST this year. else, like my case, Gold already imposed GST in Feb (anniversary month), then upgraded to Platinum in April, another GST coming in 3 months time. this was a mistake of mine, didnt know GST is charged such way
if already imposed GST for your Gold cards, then probably can upgrade next year before GST kicked in. at least you wont double-pay the GST.
'bout cashback from Gold -> Platinum, mbb told me it's same pool. let's say, today, your Gold spending already getting RM25 cashback (own calculation). Your upcoming Platinum spending will have remaining RM25 cashback till end of May. Considering the upgrade takes about 1 week, you might have about 1.5 week remaining

you still can use the Gold cards until you terminate them. In fact, you can pass the Gold cards to spouse/family to pump petrol and help you earn cashback
i did test this scenario. spent the remaining using Platninum and maxed the RM50 cashback by end April. Come 1st May, gotten RM50 cashback. RM33 cashback from Gold, RM17 from Platinum.
yeah gonna do it this august...coz my gst for current on oct.
so sad tp become 250...gt around 48xk before chg from 200>250....any idea wat else worthy to redeem except gst n voucher?
on the spot for aeon voucher the best deal i think of currently but i not live in kl...gonna do it the next time i go kl.