BIP39 vs Electrum Mnemonic seed

[o_e_l_e_o]

There was an individual who managed to brute force 4 words using custom code and renting cloud computing. It cost him $350 and took 30 hours. To scale that up to 5 words, it would cost >$700,000 and take 7 years. And this is of course assuming you are 100% certain about the other 7 words, including their order and position.

So in short, it's almost certainly not worth your time to try to brute force 5 words.