Looks like the size is 2437 bytes, or at least that's what it was for the transfer coming into my Blockchain wallet.
E
Firstly, congrats on being a rare specimen that actually learns from previous issues! Good to see you're being proactive regarding your fees!
However, data size of the inbound transaction does not automatically translate 1:1 with data size of an outbound transaction. So even though your inbound transaction was 2437 bytes, it may be that all the coins were placed into one output.
So, when you go to spend that output, your data size will be significantly reduced... possibly as low as 1x Input 148 bytes + 1x Output 34 bytes + Fixed 10 bytes = 192 bytes, or maybe 226 bytes if there is a 2nd output for any change.
Without being able to see the original transaction, it is a little difficult to tell, but if the original 2437 byte transaction resulted in all the coins going into one address, chances are, your new transaction will only be around 192-226 bytes, so calculate your fee accordingly.
On a side note, does blockchain.info allow you to modify the fees? Most users seem to claim that the reason they sent transactions with low 50 sat/byte type fees is because "Blockchain.info doesn't allow me to set the fee"