I've actually already set just about all of those, with the exception that I've turned off some of the security items just to eliminate all possible causes. So syscookies are off, loging martians is off.
Here are the settings that I've tweaked:
# Ignore ICMP broadcasts
net/ipv4/icmp_echo_ignore_broadcasts = 1
#
# Ignore bogus ICMP errors
net/ipv4/icmp_ignore_bogus_error_responses = 1
# Do not accept ICMP redirects (prevent MITM attacks)
net/ipv4/conf/all/accept_redirects = 0
# Do not send ICMP redirects (we are not a router)
net/ipv4/conf/all/send_redirects = 0
#
# Do not accept IP source route packets (we are not a router)
net/ipv4/conf/all/accept_source_route = 0
net.ipv4.tcp_fin_timeout=15
net.ipv4.tcp_max_syn_backlog = 4096
net.ipv4.tcp_synack_retries = 5
net.core.rmem_max = 16777216
net.core.wmem_max = 16777216
net.ipv4.tcp_rmem = 4096 87380 16777216
net.ipv4.tcp_wmem = 4096 65536 16777216
net.ipv4.tcp_no_metrics_save = 1
net.ipv4.ip_local_port_range = 9000 61000
net.ipv4.tcp_low_latency = 1
net.ipv4.tcp_tw_reuse = 1
net.core.somaxconn = 2048
net.ipv4.tcp_sack = 0
net.ipv4.tcp_dsack = 0
net.ipv4.tcp_tw_recycle = 1
net.ipv4.tcp_syncookies=0
fs.file-max = 253184
#added 12.13.2010 to improve latency performance
# Turn off the tcp_window_scaling
net.ipv4.tcp_window_scaling = 0
# Decrease the time default value for tcp_keepalive_time connection
net.ipv4.tcp_keepalive_time = 1800
# Increase the tcp-time-wait buckets pool size (default was 180000)
net.ipv4.tcp_max_tw_buckets = 1440000