Although not mentioning it, neither in the specification nor in the sample code, your desired output implies you want the "maximum" per $1 value.
Are you talking of $4's entire string value, or of the numerical part only? What if it starts with an "S" or an "s"?
If you go for the numerical part, try
awk '{T = $4; gsub (/[^0-9]/, "", T); if (T > a[$1]) {a[$1]=T; b[$1]=$0}}; END {for (i in b) print b}' file