How do I achieve maximum data length?

Question

Is achieving a data length of 251 possible in SDK 14.0.0, SoftDevicve S132 5.0.0 ? I tried updating my GATT table to 6000 bytes and my NRF_SDH_BLE_GATT_MAX_MTU_SIZE to 251, but I get the following errors:

<debug> ble_gatt: Requesting to update ATT MTU to 251 bytes on connection 0x0.
<debug> ble_gatt: Requesting to update data length to 255 on connection 0x0.
<error> ble_gatt: sd_ble_gap_data_length_update() (request) on connection 0x0 returned unexpected value 0x7.
<info> app: Reset challenge status on conn_handle 0x0
<info> app: Connected
<info> app: connection interval: min 15, max: 15
<debug> ble_gatt: ATT MTU updated to 185 bytes on connection 0x0 (response).
<info> app: ATT MTU exchange completed. MTU set to 185 bytes.
<info> app: Data length is 185 bytes.
<debug> ble_gatt: Peer on connection 0x0 requested a data length of 251 bytes.
<debug> ble_gatt: Updating data length to 251 bytes on connection 0x0.
<error> ble_gatt: p_dl_limitation: 101, 101, 1612
<error> ble_gatt: sd_ble_gap_data_length_update() (reply) returned unexpected value 0x13.
<info> app: Slow advertising.
<info> app: stop_motion_updates
<info> app: Disconnected