I'll concur with the others...
SA Grievous with the right torso articulation would be quite able to pull off the spider-walk. Grievous is one of those characters you just want that ONE ultimate version of. One that has pop-off hands for his fight with Obi, has a cloth robe with saber hilt pockets, super articulated that blows away any other SA figure... Even if it's a Deluxe figure, I'll pay it to get it.
Grievous and Jango Fett are two really snubbed figures for GOOD quality figures... And both deserve SA deluxe type treatment (tons of accessories, etc.).
All he would need for the pop-off hands would be wrist articulation, unless you want one with scorch marks on his wrists. I think an SA Greivous would be hard for Hasbro, but still doable.