Hello, wow what a great build, I have to complement your component choices.
Last year I built my computer about two years ago (I-7 2600K CPU) and I used a Corsair GT 120 GB for the OS drive. On that drive I only put Windows 7 and programs. For storage I have a 1.5 TB and a 1 TB HDD.
I had an I7 920 CPU based computer before this one and it used a HDD to run the OS. This computer was considered to be very fast in its day. I can tell you that the difference is really night and day - the SSD system. The SSD computer just blows away the non-SSD computer.
It is hard to explain until you actually use an SSD for your operating system but EVERYTHING works faster. Boot times are wicked fast , EVERY program loads instantly, even the resource hogs like MS Office and CAD programs. I am not a gamer but I hear most games load almost instantly also and they are major resource hogs.
I got a OCZ Vertex 4 128 GB to use as a backup drive from Newegg on sale for $75.00 and it is blazing fast.
While no one can make the decision for you, I can strongly recommend that going with at least a 120 GB SSD for your operating system is a great investment. The time that it will save you over the years will more than pay you back.
SSDs are exploding in sales for a good reason, they are just flat out faster. And they will probably turn out to be more reliable also because they have no moving parts.
If cost is an issue, check Newegg and Amazon for sales and you will be able to get a great deal on a 120 GB or a 128 GB SSD for your operating system. Just make sure it is SATA III.
The Samsung 840 Pro Series 128 GB or 256 GB is probably the fastest one out there right now but the top SSDs are all fairly close to each other in performance and Tom's has an SSD guide that is pretty good. So you can look for a sale and buy a cheap SSD and you won't get burned because it will be just about as fast as the 840 Pro.
The OCZ Vertex 4 goes on sale a lot and the their new Vector series is very fast. The Corsair GT is also great - I own it and it is very fast.
Good luck with your choice. Going with an SSD is worth it so save up your Starbucks money.