I would like to practice in CW on 2m/70cm bands when and if there will be a tropospheric or sporadic-E propagation. However I don't have mush space for the antenna. There is a possibility to install 3+5 el Uda-Yagi antenna on the balcony (the height is ~20 meters), which has 9.5 dBi gain on 2m and 11.15 dBi gain on 70cm in free space according to the manufacturer. Previously I successfully used this antenna to make SAT QSOs in FM. My QTH is Russia, Moscow, the balcony looks southwest (i.e. to Europe), the horizon is quite clear.
Assuming that I'm going to use 50W of power (e.g. Yaesu FT-991A), will the antenna be adequate for making CW QSOs? If not, what gain approximately is required? Would it help to use a 200W power amplifier on 2m?