F5 (FFIV) beat fiscal fourth-quarter targets but guided in-line for the current quarter and said its sales chief will leave next month.The Seattle Web switchmaker posted an adjusted profit of 31 cents a share. That number compares with pro forma earnings of 29 cents a share in the year-ago period. Sales for the fiscal fourth quarter ended last month were $145.6 million, up 10% from $132.4 million in the prior quarter and 30% above the $111.7 million level a last year. Analysts were looking for adjusted profit of 11 cents a share on $144 million in revenue, according to Yahoo Finance. The news comes a mere 24 hours after Internet gearmaking rival Riverbed ( RVBD) reported disappointing numbers that sent the shares down 27% Wednesday. Looking ahead, F5 says it expects fiscal first-quarter earnings to be around 21 cents on $155 million in sales. That forecast is roughly in line with analysts expectations. F5 shares fell $3.76, or 9%, to $36.71 in after-hours trading Wednesday.