4" or 5" Senko or other rod that you would suggest

610MLXF or 68MXF if you want a little more rod. I really like St. Croix's MLXF for finesse. 

I use a 610MLXF as well. Such a great rod. I've also been a big fan of St. Croix spinning rods

I use an avid 68mxf, its a softer xf tip than the LT's 6'10mxf so it'll work much better for 4" and 5".

Personal opinion. Not a big fan of xf tips for senkos. The medium fasts feel a bit "sitffer" to me and when they grap that t rigged senko I like to stick it to them. I'd look at a 6'6 or 7' medium fast If we are talking senkos or any other t rigs over 1/4oz.

After fishing the Avid and the LTB 6'8" for years, I switched fairly recently. My sole issue with the XF rods in both series is they are overpowered by a 4" senko on the cast. Let alone a 5". They're adequate, but not perfect. I went to the 6-10 Shakeyhead rod fairly recently, and have been blown away at the efficacy. I hadn't fished any of the other St Croix because I had my Loomis sticks. The 6-10 is the perfect finesse rod, outside of drop shot applications.

I'll never look back after fishing the 6-10.

I think it's been brought up a few times is a 5 inch senko really a finesse bait? To me it's not.