Here are my thoughts ...
Fernando - When he played for Madrid alongside Raul many years ago he was a very good player. He had power, energy and was hungry. He won his fair share with Madrid, but then they got Ronaldo and they had Portillo so the decided to loan him to Monaco. There he arrived on good form and with a big reputation. A player coming from Real Madrid to a club who had no noticeably world class talent was always going to lift the squad and perform well. He knocked out Madrid in the CL and had a good loan spell with Monaco.
Then Madrid realized that they had made a mistake, just like with Eto'o and Makelele and Cassano - so they brought him back, only for him to sit on the bench. This is where he started to loose confidence, just a year ago he knocked out Madrid in the CL and here he found himself on the Madrid bench not worthy of getting a chance in the starting lineup. He was never ahead of El Capitan Raul and superstar Ronaldo. Owen was also above him in the peaking order and Luxembergo really didn’t think Fernando had anything worthy to offer. So they sold him to Liverpool. Last season he was very poor. Everyone was patient and thought with a full pre-season he will regain his form and start to shine (as many new players do). But it was not to be, so far what I have seen of him I don’t think he is anywhere better than what he was last season. He is no where close to the form he was in at Monaco. He plays with his back to goal and finds it difficult to get the ball out of his feet.
The thing is, in modern football there is a lot more expected out of the forward/striker. You look at the top teams in the EPL. Henry and Bergkamp who lead the line for Arsenal are always dropping back and helping out in defense and creativity. At Manu Rooney is always all over the pitch and really plays as a footballer as opposed to an out and out striker, RVN is the out and out striker but he too drops back central MF to allow Rooney and Park to get forward. At Chelsea Drogba does a lot of tracking back and making space for others.
I don’t think Fernando has that in him, maybe he can cut it in Spain or Italy but deffo not in the EPL. He finds it difficult to be at par with the pace of the game, he doesn’t really track back and help out (that maybe down to tactics). He doesn’t do a lot of things - and without the need to pin point what they are I can broadly say he isn’t the correct hard working CF.
Cisse - Had a good season with his pervious club. He was on fire last season until he broke his leg. Its very difficult to come back form such an injury, but yet what he has offered and what he has shown since his return is much more than what Fernando has shown. He is the fastest player at Liverpool and one of the fastest in the EPL, if you have to break into a quick counter attack its him who will outrun everyone (including the ref

I guess what im trying to say is - selling Cisse will be a huge mistake.
Chelsea Forever.