I don't think you asses Welsh as not being overly impressive without him having a proper run in the first team, which, perhaps because of his similarities to Gerrard, he's never had. Remember, he's th captain of the U21 England team, so he can't be that bad!
Do you not think that it might be betterfor welsh to go on loan? Like kieran Richardson. Maybe Sunderland, wigan or west ham could take him.
I never said welsh is bad, i can only judge him on when I saw him play for the first team. FSP looks like an excellent, young skillful prospect and looked very good in the pre-season, but he also didn't manage to utilise him ability (not fully yet) in his prem appearances.
Diarra is bit further ahead in his career, a good season at Lens and an international call up. If Rafa plays 4231/4411, then a proven defensive midfielder in the squad would be my preference.