diff --git a/src/core/config/mod.rs b/src/core/config/mod.rs
index 14e8fa29..e19a5974 100644
--- a/src/core/config/mod.rs
+++ b/src/core/config/mod.rs
@@ -1823,9 +1823,9 @@ pub struct Config {
 	pub stream_amplification: usize,
 
 	/// Number of sender task workers; determines sender parallelism. Default is
-	/// '4'. Override by setting a different value. Values clamped 1 to core count.
+	/// core count. Override by setting a different value.
 	///
-	/// default: 4
+	/// default: core count
 	#[serde(default = "default_sender_workers")]
 	pub sender_workers: usize,
 
@@ -2059,40 +2059,41 @@ fn default_db_write_buffer_capacity_mb() -> f64 { 48.0 + parallelism_scaled_f64(
 
 fn default_db_cache_capacity_mb() -> f64 { 512.0 + parallelism_scaled_f64(512.0) }
 
-fn default_pdu_cache_capacity() -> u32 { parallelism_scaled_u32(50_000).saturating_add(500_000) }
+fn default_pdu_cache_capacity() -> u32 { parallelism_scaled_u32(50_000).saturating_add(100_000) }
 
 fn default_cache_capacity_modifier() -> f64 { 1.0 }
 
 fn default_auth_chain_cache_capacity() -> u32 {
-	parallelism_scaled_u32(50_000).saturating_add(500_000)
+	parallelism_scaled_u32(50_000).saturating_add(100_000)
 }
 
 fn default_shorteventid_cache_capacity() -> u32 {
-	parallelism_scaled_u32(100_000).saturating_add(500_000)
+	parallelism_scaled_u32(100_000).saturating_add(100_000)
 }
 
 fn default_eventidshort_cache_capacity() -> u32 {
-	parallelism_scaled_u32(100_000).saturating_add(500_000)
+	parallelism_scaled_u32(50_000).saturating_add(100_000)
 }
 
 fn default_eventid_pdu_cache_capacity() -> u32 {
-	parallelism_scaled_u32(50_000).saturating_add(500_000)
+	parallelism_scaled_u32(50_000).saturating_add(100_000)
 }
 
 fn default_shortstatekey_cache_capacity() -> u32 {
-	parallelism_scaled_u32(50_000).saturating_add(500_000)
+	parallelism_scaled_u32(50_000).saturating_add(100_000)
 }
 
 fn default_statekeyshort_cache_capacity() -> u32 {
-	parallelism_scaled_u32(50_000).saturating_add(500_000)
+	parallelism_scaled_u32(50_000).saturating_add(100_000)
 }
 
 fn default_servernameevent_data_cache_capacity() -> u32 {
-	parallelism_scaled_u32(200_000).saturating_add(500_000)
+	parallelism_scaled_u32(100_000).saturating_add(100_000)
 }
 
 fn default_stateinfo_cache_capacity() -> u32 {
-	parallelism_scaled_u32(500).clamp(100, 12000) }
+	parallelism_scaled_u32(500).clamp(100, 12000)
+}
 
 fn default_roomid_spacehierarchy_cache_capacity() -> u32 {
 	parallelism_scaled_u32(500).clamp(100, 12000) }
@@ -2312,7 +2313,7 @@ fn default_stream_width_scale() -> f32 { 1.0 }
 
 fn default_stream_amplification() -> usize { 1024 }
 
-fn default_sender_workers() -> usize { 4 }
+fn default_sender_workers() -> usize { parallelism_scaled(1) }
 
 fn default_client_receive_timeout() -> u64 { 75 }
 
diff --git a/src/service/rooms/event_handler/upgrade_outlier_pdu.rs b/src/service/rooms/event_handler/upgrade_outlier_pdu.rs
index cbebee4b..5c60ab71 100644
--- a/src/service/rooms/event_handler/upgrade_outlier_pdu.rs
+++ b/src/service/rooms/event_handler/upgrade_outlier_pdu.rs
@@ -159,6 +159,8 @@ pub(super) async fn upgrade_outlier_to_timeline_pdu(
 		.collect()
 		.await;
 
+	if extremities.len() == 0 { info!("Retained zero extremities when upgrading outlier PDU to timeline PDU with {} previous events, event id: {}", incoming_pdu.prev_events.len(), incoming_pdu.event_id) }
+	
 	debug!(
 		"Retained {} extremities checked against {} prev_events",
 		extremities.len(),