I'd just go to AA's Greenwich lounge in T8 and not deal with going through security twice and crowded lounges in T4. The CL speakeasy may have slightly nicer cocktails but could be busy and the VS lounge may let you in with Venture X (or could cite crowding and may not let you in, plus it's mixed results on whether they still accept CC entrances), but not worth dealing with T4's long-ish security (inc precheck and clear) to find out.