This is OT and I apologize to the community in advance... but since it was asked.....
The Intel 320 is basically an upgraded X25-m (might as well call this one the X25m gen 3). Great bang for your buck drive...but I wouldnt put it in the same category as the M4 where its a sata 2. BUT it is great for its price (actually its one of my main picks for rigs where sata 2 is the only option...or only option where sata 6gb/s ports result in NO trim).
The Intel 510 is basically the same as M4 except it uses a custom firmware (like crucial, Intel rolls thier own firmware). The biggest dif is the firmware has over-provisioning built in (with all SSDs...I format them smaller then they. For example my 256GB M4 is a 220GB'er in my 890 to give LOTS of room for firmware to work with..but I am ULTRA conservative and never fill a drive to more than 60-70 percent. As Tony on OCZ once said: when I need more room, I stick in a bigger drive.). Biggest thing the 510 has is 5K erase cycle nand. Of course, peeps have proven that Crucial is being ultra conservative with their 3K specification and have used a M4 to well over 5K avg...and its still kicking.
Is the increase in price of the 510 worth it over the M4? Depends. Both have killer CS, both have great firmware...both are great drives. So its all personal pref which way to go. Personally I consider them both to be best in class on long term reliability and performance. YMMV
If you mean the upcoming 520 / 710 / 720...no idea. Wont know till they officially land.