I use SAM4 on my station
2NG, it functions well, does what I need it to for the most part. However, what I do want is good Voice-tracking. The VT function that was added in V4 is basic by even the most loosest standards. Simply it will record from the sound card and allow ultra-basic editing (delete before/after position). Truth is I don't find it useful at all because I can't preview through it (I use the Rear channels on a 5.1 card to preview and the VT will play on the main audio!)
The other upgrade benefits are that it now includes a licensed AAC+ encoder and the Bid4Spots/StreamAdz integration, although for some of us, that had become somewhat of a damp squib, primarily due to the very low CPM rates it attracted and also, for those of us licensed by Loudcity, the new agreement with SESAC currently prevents us from running instream ads.
Finally what is useful, for me at least, you can now make use of on-board DSP such as compressor/limiting if you have an Orban card or E-MU 1212M which I will be adding, hopefully this weekend!
I wouldn't upgrade for Voice-tracking, it's extremely early days for that, if you need AAC+ or Bid4Spots/StreamAdz integration then it may be worth it.
It is however stable in my view.