Bittrex is literaly running out of STEEM and this pushes the prices higher and higher. If you want to invest in Steem maybe it is good advice to take a step back and breath, if you want to buy after this - go on!
Do you need to invest right now in STEEM?
Yes - go to Bittrex and buy
No - you should wait and a couple of days and look how the push to higher grounds is working
Do you need to get more STEEM to Power Up?
Yes - go straight to Bittrex and buy right now
No - If you have time you should wait
To rush is probably not a good strategy. If you really need to buy right now, you should split your investment and buy overt the next days. Maybe this will cost you, but maybe it will save you also a lot of money.