I also have Solo Spot Light Strings, but have yet to use it. [K5 for that one.]
 
Concert Strings 2 includes 'Solo Strings 2' already.
 

Just looking at the requirements list and it's kind of confusing.
 
I'd want to contact Kirk just to be sure. There's still 4 days left for the sale to do so.

Kirk said he's coming out with a new library by the end of the year. You might want to wait for that before you decide. It has fully controllable vibrato. You can control the speed and depth in real time, just like Spotlight solo strings, but this is ensemble and solo instruments. It sounds better than his older libraries too, but I haven't heard much of it yet. I hope he posts more clips soon.
 
https://www.youtube.com/watch?v=p41B18WkyHs
 
You can hear how it sounds there. The feature set is amazing and the sound very good IMO, but I'd like to hear the other instruments and the solos too. Looks like I'll be dropping some more money soon.

Chandler
Kirk said he's coming out with a new library by the end of the year. You might want to wait for that before you decide. It has fully controllable vibrato. You can control the speed and depth in real time...

A few things to note:
 
1. The thing to ask him though, is will this new library be for K4 or K5?
 
Because of K5's new scripting abilities, many are now writing for that version, instead of K4.
 
Kirk did this for Spot Light Strings.
 
Bit doesn't have K5.
 
2. Concert Strings 2 has controllable vibrato as well, which is why I went for it over GPO.
 
3. Kirk offers upgrade paths which I believe are just the price differences, so one could get CS 2 if it still works in K4, and always upgrade later. That way, the sale price can be had for now, and in case the new library is only for K5, then Concert Strings 2 was the safe purchase to go with right now while on sale.
 
 

I saw that announcement, too, but so far there has been no further information from the vendor regarding Kontakt compatibility or upgrade pricing. All the more reason for me to jump on CS2 now. If it turns out I can use CS3, I'm sure there'll be an upgrade offer. And if I can't use CS3 without also upgrading Kontakt, I'll still have a version that I can use (that may no longer be available after CS3). 
 
At this point, I'm inclined to call it my Christmas present and go for CS2. The main thing that makes me hesitate is that I see no option for buying it on DVDs rather than downloading. After my last download fiasco with ST3, I'm determined to not obtain any more 30GB libraries via DSL. They do offer to ship it on a hard drive, but that seems excessive. A USB stick would be nice, though.

Some more information about SC3 here: http://www.kirkhunterstudios.com/cs3.html
 
Some cool new features:

• Mic distance from 5 to 38 feet
• Loosen each player's entrance
• Run and fill sequencer
• Full vibrato control
• Individual volume and panning for each instrument in an ensemble
• New articulations (e.g. Dolce Largo, I don't know what it is but I'm going to look it up)

Still no firm release date or pricing information, though.
 

bitflipper
...All the more reason for me to jump on CS2 now. If it turns out I can use CS3, I'm sure there'll be an upgrade offer. And if I can't use CS3 without also upgrading Kontakt, I'll still have a version that I can use (that may no longer be available after CS3)...
 

Exactly.
But he does seem to offer upgrades, and looking at the new features below, I may go for it as well when the times comes.

bitflipper
At this point, I'm inclined to call it my Christmas present and go for CS2. The main thing that makes me hesitate is that I see no option for buying it on DVDs rather than downloading. After my last download fiasco with ST3, I'm determined to not obtain any more 30GB libraries via DSL. They do offer to ship it on a hard drive, but that seems excessive. A USB stick would be nice, though.

I didn't have any problems with the download. Some burn them to DVDs to have a physical copy, but I just have an external USB 3.0 Hard Drive that I store all my VSTs on as master copies.  I paid $99 for it for 1TB.

bitflipper
I skipped the K5 upgrade even when it was $49 because the update brought almost nothing new to the game - not even any new factory content - and my favorite library developers were/are still K4-compatible.

I think that the enhanced scripts, the new filters, and Retro Machines is well worth $49

Lots of folks think so. I don't.
 
I can't name one commercial library that makes use of the new scripting features. The main reason new libraries are K5-only is that they are latecomers, and NI makes it impossible to create a K4-compatible library unless you already own K4, which they won't sell to you.

I wonder if EastWest Hollywood isn't a possible competitor here, now you can combine BOGOF and an additional $100 discount ?