You and I have actually spoken about this before, I think. To tell you the truth, of the 4E's I've played and the 1a's, there's not enough of a gap between them performance-wise (IMHO) to justify a model in between. The 1a's that I've played (in general) have had a little more projection and volume and maybe a little more strength and focus in the trebles....but then, some have been no better, really. The best 4E I've ever played, I bought (on the spot and for a bargain at $1,900 new)..and I still own it. That one's not going anywhere....I've only played a couple of 1a's that I'd choose over it. It's not a 1a, but it will compare as favorably as you could expect.
All that having been said, I've never played an SP, but I just can't see the justification. If a 4E wouldn't do the trick for me, I'd go ahead and spend $6,500 or $7,000 for a good used 1a Tradicional before I'd spend $5,000 on the SP. I've actually seen a couple of 664mm 1a's on e - b a y that could have been picked up for less than $4,000 and a couple of 650mm that could have been won for $5,000 or so.
I'll tell you what, though....if you're looking for a bargain in a Ramirez, check out the Anos 125 Anniversary model. It's a solid IR and Cedar Ramirez based on the "E" series platform (although the headstock looks decidedly "R" series to me). GSI is selling them for $1,999.00. I haven't played one, but I wonder how it compares to the 4E......nah....I need another CG like I need another hole in my head......