lost many time on youtube, read some reviews and finally i'm here. what's your can say about this hard choice?

RX-7 give you all the official yamaha RAM cart sounds in the ROM.
RX-7 has simple beat and DSP efx.

RX-5 allows you to tweak the samples much more.
RX-5 has reverse button.
RX-5 has individual outputs and mixer.
RX-5 can allow for user samples with a 3rd part programmable cartridge.

Both are way to big.
The RX5 is a much better machine, but costs 4x as much.

If you see a good deal on an RX-5 and you love drum machines, it's worth picking up.

Neither one is particularly essential.
All the samples in the RX-7 are available in good quality on the web.

Similar, perhaps more interesting, and more overlooked is the korg S3 (also much worse to program).

RX7 receives and sends sysex (parameters). RX5 does not.

i quite liked the RX7. had both at the same time and had to choose, literally for the sake of space, they are big. kept the (bigger) RX5, um, because it's like some design trip back to the 80s console. and has multiple outputs.

pattern/song memory is eaten up pretty much in one session.