If you use the 50 W CW KIT amp from Qrp Labs (about $30 USD) you will get 14 W true out on 40 M with a 14 V supply. that 's another 5.5 dB of signal at the far end. That amp will produce 45 W but only on a 22 VDC supply. It is specifically designed for QSK CW work though mods to make it a SSB amp are possible.
If you equip it with "bend pin " RD16HH mosfets you will get up to 20 W of clean CW rf out on 40 mtrs. THe efficiency will be about 55 percent. The RD16HHs can be got for about $12 a pair from Ebay Schenzen etc (if you go too cheap you will get fakes ) . Hans Summers ex Qrp labs does not sell those parts . THe RD16s are vastly better from a thermal point of view.
NB you need to get an RX / TX 5V TTL signal out of the BJ to the power amp to control it the rx tx switching . that could be an issue - you may need to fit a TDO timer (CMOS 555) based on the CW key down so you will get only semi qsk in that case.
The 50W CW amp is one off the deals of the century in terms of what you get for the money. The only ones that don't work are the ones where someone on cocaine wound the RF transformers or soldered the puppy up. If you do build one, consider fitting dpdt relays and a second filter set so you make it dual band.