Hello and welcome to the forum.
As far as i know the speed of the card will be most effective when you will be in the process to download your data into your computer.So take this into consideration when you estimate the amount of money you want to spend.There are several classes of SD cards, the higher class the better overall speed and performance.You should consider also the type of files that you want this sd card to store for example if you shoot raw you need a high class sd in order to transfer your data faster or if you plan to capture HD video.
Overall i don't think that a high speed card would be a bad choice but remember to check panasonic's site for full list of compartible sd cards before you make the purchase.
I think you may have misunderstood his question as the OP seems to be aware of the benefits of a faster card. What he's asking is whether the transfer speed when writing from the camera to the card is quick enough that having a 45MB/s (write speed) SD card is beneficial or if it's so "slow" that a 45MB/s write speed on the card is overkill so you'd be better off with a 30MB/s card.