How to continue operation with comp-lzo and/or migrate from it?

Dear listusers,

on a flavor we have

- clients with comp-lzo in their local config and we have no access to 
this clients. (can't change it)

- very old clients below 2.3 (no peer info)

- also "modern" clients of all versions 2.3.2 - 3.8.5


Our minimum Cipher is AES-256-CBC as fallback, when does AES-256-CBC is 
supported by openvpn? It could reveal the minimum client version.


--allow-compression asym

can be set, but clients will still compress. Clients without, can't connect.


--compress migrate

clients > 2.3 get pushed "stub-v2" all other "comp-lzo no".

What happens to clients wich does not support it? e.g. 2.2.x

This parameter is not documented in the reference manual, it is still 
supported in 2.6 and how long it may be supported?


What could be the best way to operate it with a little attack surface 
(voracle) but remaining compatibility for old clients?


Thanks for all information on this topic.